485BPOS

As filed with the Securities and Exchange Commission on April 7, 2014

File No. 333-108472

811-21425

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933	x
Pre-Effective Amendment No.	¨
Post-Effective Amendment No. 25	x
and/or
REGISTRATION STATEMENT
UNDER
THE INVESTMENT COMPANY ACT OF 1940	x
Amendment No. 27	x

(Check appropriate box or boxes)

PIONEER SERIES TRUST I

(Exact Name of Registrant as Specified in Charter)

60 State Street, Boston, Massachusetts 02109

(Address of Principal Executive Offices) (Zip Code)

Registrant’s Telephone Number, including Area Code: (617) 742-7825

Terrence J. Cullen, Pioneer Investment Management, Inc.

60 State Street, Boston, Massachusetts 02109

(Name and Address of Agent for Service)

It is proposed that this filing will become effective (check appropriate box):

x immediately upon filing pursuant to paragraph (b)

¨ on [date] pursuant to paragraph (b)

¨ 60 days after filing pursuant to paragraph (a)(1)

¨ on [date] pursuant to paragraph (a)(1)

¨ 75 days after filing pursuant to paragraph (a)(2)

¨ on [date] pursuant to paragraph (a)(3)of Rule 485.

If appropriate, check the following box:

¨ This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, the Trust certifies that it meets all of the requirements for effectiveness of this registration statement under Rule 485(b) under the Securities Act and has duly caused this Post- Effective Amendment No. 25 to its registration statement to be signed on its behalf by the undersigned, duly authorized, in the City of Boston, and the Commonwealth of Massachusetts, on the 7th day of April, 2014.

	PIONEER SERIES TRUST I
By:	/s/ Daniel K. Kingsbury
	Daniel K. Kingsbury
	President

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed below by the following persons in the capacities indicated below on April 7, 2014:

	Signature	Title
	Mark E. Bradley*	Treasurer (Principal Financial and Accounting Officer)
	Mark E. Bradley
	David R. Bock*	Trustee
	David R. Bock
	Benjamin M. Friedman*	Trustee
	Benjamin M. Friedman
	Margaret B. W. Graham*	Trustee
	Margaret B. W. Graham
	/s/ Daniel K. Kingsbury	President (Principal Executive Officer) and Trustee
	Daniel K. Kingsbury
	Marc O. Mayer*	Trustee
	Marc O. Mayer
	Thomas J. Perna*	Chairman of the Board and Trustee
	Thomas J. Perna
	Marguerite A. Piret*	Trustee
	Marguerite A. Piret
	Kenneth J. Taubes*	Trustee
	Kenneth J. Taubes
	Stephen K. West*	Trustee
	Stephen K. West
By:	/s/ Daniel K. Kingsbury
	Daniel K. Kingsbury	Dated: April 7, 2014
	Attorney-in-Fact

EXHIBIT INDEX

Exhibit No.	Description
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	PIONEER SERIES TRUST I
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Pioneer Oak Ridge Large Cap Growth Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	PIONEER OAK RIDGE LARGE CAP GROWTH FUND
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Capital appreciation.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the fund. You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Pioneer funds. More information about these and other discounts is available from your investment professional and in the "Sales charges" section of the prospectus beginning on page 36 and the "Sales charges" section of the statement of additional information beginning on page 53.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	SHAREOWNER FEES (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	PORTFOLIO TURNOVER
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 16% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	16.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Pioneer funds.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the fund for the time periods shown and then, except as indicated, redeem all of your shares at the end of those periods. It also assumes that (a) your investment has a 5% return each year and (b) the fund's total annual operating expenses remain the same except for year one (which considers the effect of the expense limitation). Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example by, Year, Caption [Text]	rr_ExpenseExampleByYearCaption	IF YOU REDEEM YOUR SHARES NUMBER OF YEARS YOU OWN YOUR SHARES
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	IF YOU DO NOT REDEEM YOUR SHARES NUMBER OF YEARS YOU OWN YOUR SHARES
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Normally, the fund invests at least 80% of its net assets (plus the amount of borrowings, if any, for investment purposes) in equity securities of large capitalization companies. Large capitalization companies have market capitalizations at the time of acquisition of $3 billion or more. The fund anticipates that the average weighted market capitalization of the companies in the fund's portfolio will be significantly higher than $3 billion. The equity securities in which the fund principally invests are common stocks, preferred stocks and depositary receipts, but the fund may invest in other types of equity securities to a lesser extent, such as exchange-traded funds (ETFs) that invest primarily in equity securities, equity interests in real estate investment trusts (REITs), warrants and rights. The fund may invest in initial public offerings of equity securities. The fund may invest up to 20% of its total assets in equity and debt securities of non-U.S. issuers. The fund will not invest more than 10% of its total assets in the securities of emerging markets issuers. The fund may invest in debt securities. The fund may invest up to 5% of its net assets in below investment grade debt securities (known as "junk bonds"), including below investment grade convertible debt securities and securities of issuers that are in default. The fund may, but is not required to, use derivatives, such as stock index futures and options. The fund may use derivatives for a variety of purposes, including; in an attempt to hedge against adverse changes in the market prices of securities, interest rates or currency exchange rates; as a substitute for purchasing or selling securities; to attempt to increase the fund's return as a non-hedging strategy that may be considered speculative; and to manage portfolio characteristics. The fund may choose not to make use of derivatives for a variety of reasons, and any use may be limited by applicable law and regulations. The fund may also hold cash or other short-term instruments. The fund uses a "growth" style of management and seeks to invest in issuers with above average potential for earnings growth. When making purchase decisions for the fund, the subadviser uses a disciplined approach that involves three primary components: Research - The subadviser analyzes research on potential investments from a wide variety of sources, including internally generated analysis and research provided by institutions and the brokerage community. Fundamentals - Once a potential investment is identified, the subadviser considers whether the issuer possesses certain attributes that the subadviser believes a "buy" candidate should possess. Valuation - Finally, the subadviser values companies by considering price-to sales ratios and price-to-earnings ratios within a peer group. From this process, the subadviser constructs a list of securities for the fund to purchase. The subadviser makes sell decisions for the fund based on a number of factors, including deterioration in a company's underlying fundamentals and better relative value in other securities.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS OF INVESTING IN THE FUND
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	You could lose money on your investment in the fund. As with any mutual fund, there is no guarantee that the fund will achieve its objective. MARKET RISK. The values of securities held by the fund may go up or down, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic, political, or regulatory conditions, inflation, changes in interest or currency rates, lack of liquidity in the bond markets or adverse investor sentiment. Adverse market conditions may be prolonged and may not have the same impact on all types of securities. The values of securities may fall due to factors affecting a particular issuer, industry or the securities market as a whole. The stock market may perform poorly relative to other investments (this risk may be greater in the short term). High public debt in the U.S. and other countries creates ongoing and systemic market risks and policymaking uncertainty. The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities worldwide. Governmental and non-governmental issuers have defaulted on, or been forced to restructure, their debts, and many other issuers have faced difficulties obtaining credit. These market conditions may continue, worsen or spread, including in the U.S., Europe and beyond. Further defaults or restructurings by governments and others of their debt could have additional adverse effects on economies, financial markets and asset valuations around the world. In response to the crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support financial markets, including by keeping interest rates at historically low levels. More recently, the Federal Reserve has reduced its market support activities. Further reduction or withdrawal of this support, failure of efforts in response to the crisis, or investor perception that these efforts are not succeeding could negatively affect financial markets generally as well as increase market volatility and reduce the value and liquidity of certain securities. Whether or not the fund invests in securities of issuers located in or with significant exposure to countries experiencing economic and financial difficulties, the value and liquidity of the fund's investments may be negatively affected. In addition, policy and legislative changes in the U.S. and in other countries are affecting many aspects of financial regulation. The impact of these changes on the markets, and the practical implications for market participants, may not be fully known for some time. The fund may experience a substantial or complete loss on any individual security or derivative position. GROWTH STYLE RISK. The fund's investments may not have the growth potential originally expected. Growth stocks may fall out of favor with investors and underperform the overall equity market. PORTFOLIO SELECTION RISK. The subadviser's judgment about a particular security or issuer, or about the economy or a particular sector, region or market segment, or about an investment strategy, may prove to be incorrect. RISKS OF NON-U.S. INVESTMENTS. Investing in non-U.S. issuers, or in U.S. issuers that have significant exposure to foreign markets, may involve unique risks compared to investing in securities of U.S. issuers. These risks are more pronounced for issuers in emerging markets or to the extent that the fund invests significantly in one region or country. These risks may include different financial reporting practices and regulatory standards, less liquid trading markets, extreme price volatility, currency risks, changes in economic, political, regulatory and social conditions, sustained economic downturns, financial instability, tax burdens, and investment and repatriation restrictions. Lack of information and less market regulation also may affect the value of these securities. Withholding and other non-U.S. taxes may decrease the fund's return. Non-U.S. issuers may be located in parts of the world that have historically been prone to natural disasters. Investing in depositary receipts is subject to many of the same risks as investing directly in non-U.S. issuers. Depositary receipts may involve higher expenses and may trade at a discount (or premium) to the underlying security. RISKS OF INVESTMENTS IN REITS. Investments in real estate securities are affected by economic conditions, interest rates, governmental actions and other factors. In addition, investing in REITs involves unique risks. They are significantly affected by the market for real estate and are dependent upon management skills and cash flow. REITs may have lower trading volumes and may be subject to more abrupt or erratic price movements than the overall securities markets. Mortgage REITs are particularly subject to interest rate and credit risks. In addition to its own expenses, the fund will indirectly bear its proportionate share of any management and other expenses paid by REITs in which it invests. Many real estate companies, including REITs, utilize leverage. RISKS OF WARRANTS AND RIGHTS. If the price of the underlying stock does not rise above the exercise price before the warrant expires, the warrant generally expires without any value and the fund loses any amount it paid for the warrant. The failure to exercise subscription rights to purchase common shares would result in the dilution of the fund's interest in the issuing company. RISKS OF CONVERTIBLE SECURITIES. The market values of convertible securities tend to decline as interest rates increase and, conversely, to increase as interest rates decline. A downturn in equity markets may cause the price of convertible securities to decrease relative to other fixed income securities. DEBT SECURITIES RISK. Factors that could contribute to a decline in the market value of debt securities in the fund include rising interest rates, if the issuer or other obligor of a security held by the fund fails to pay principal and/or interest, otherwise defaults or has its credit rating downgraded or is perceived to be less creditworthy or the credit quality or value of any underlying assets declines. Junk bonds involve greater risk of loss, are subject to greater price volatility and are less liquid, especially during periods of economic uncertainty or change, than higher quality debt securities; they may also be more difficult to value. Junk bonds have a higher risk of default or are already in default and are considered speculative. MARKET SEGMENT RISK. To the extent the fund emphasizes, from time to time, investments in a market segment, the fund will be subject to a greater degree to the risks particular to that segment, and may experience greater market fluctuation than a fund without the same focus. DERIVATIVES RISK. Using stock index futures and options and other derivatives can increase fund losses and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves behave in a way not anticipated by the fund. Using derivatives may increase the volatility of the fund's net asset value and may not provide the result intended. Derivatives may have a leveraging effect on the fund. Some derivatives have the potential for unlimited loss, regardless of the size of the fund's initial investment. Changes in a derivative's value may not correlate well with the referenced asset or metric. The fund also may have to sell assets at inopportune times to satisfy its obligations. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. New regulations are changing the derivatives markets. The regulations may make using derivatives more costly, may limit their availability, or may otherwise adversely affect their value or performance. For derivatives that are required to be traded through a clearinghouse or exchange, the fund also will be exposed to the credit risk of the clearinghouse and the broker that submits trades for the fund. It is possible that certain derivatives that are required to be cleared, such as certain swap contracts, will not be accepted for clearing. In addition, regulated trading facilities for swap contracts are relatively new; they may not function as intended, which could impair the ability to enter into swap contracts. The extent and impact of the new regulations are not yet fully known and may not be for some time. RISKS OF INITIAL PUBLIC OFFERINGS. Companies involved in initial public offerings (IPOs) generally have limited operating histories, and prospects for future profitability are uncertain. Information about the companies may be available for very limited periods. The market for IPO issuers has been volatile, and share prices of newly public companies have fluctuated significantly over short periods of time. Further, stocks of newly-public companies may decline shortly after the IPO. There is no assurance that the fund will have access to IPOs. The purchase of IPO shares may involve high transaction costs. RISKS OF INVESTMENT IN OTHER FUNDS. Investing in other investment companies, including exchange-traded funds (ETFs), subjects the fund to the risks of investing in the underlying securities or assets held by those funds. When investing in another fund, the fund will bear a pro rata portion of the underlying fund's expenses, in addition to its own expenses. LEVERAGING RISK. The value of your investment may be more volatile and other risks tend to be compounded if the fund borrows or uses derivatives or other investments, such as ETFs, that have embedded leverage. Leverage generally magnifies the effect of any increase or decrease in the value of the fund's underlying assets or creates investment risk with respect to a larger pool of assets than the fund would otherwise have, potentially resulting in the loss of all assets. Engaging in such transactions may cause the fund to liquidate positions when it may not be advantageous to do so to satisfy its obligations or meet segregation requirements. EXPENSE RISK. Your actual costs of investing in the fund may be higher than the expenses shown in "Annual fund operating expenses" for a variety of reasons. For example, expense ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile. Please note that there are many other factors that could adversely affect your investment and that could prevent the fund from achieving its goals. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text]	rr_RiskLoseMoney	You could lose money on your investment in the fund.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	THE FUND'S PAST PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table indicate the risks and volatility of an investment in the fund by showing how the fund has performed in the past. The bar chart shows changes in the performance of the fund's Class A shares from calendar year to calendar year. The table shows the average annual total returns for each class of the fund over time and compares these returns to the returns of the Standard & Poor's 500 Index and the Russell 1000 Growth Index, each a broad-based measure of market performance that has characteristics relevant to the fund's investment strategies. You can obtain updated performance information by visiting https://us.pioneerinvestments.com/performance or by calling 1-800-225-6292. The fund acquired the assets and liabilities of Oak Ridge Large Cap Equity Fund (the predecessor fund) on February 13, 2004. As a result of the reorganization, the fund is the accounting successor of the predecessor fund. In the reorganization, the predecessor fund exchanged its assets for Class A shares of the fund. The performance of Class A, Class B and Class C shares of the fund is the net asset value performance of the predecessor fund's shares prior to the reorganization, restated to reflect differences in any applicable sales charges and Rule 12b-1 fees (but not other differences in expenses). This adjustment had the effect of reducing the previously reported performance of the predecessor fund. The fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. The bar chart does not reflect any sales charge you may pay when you buy fund shares. If this amount was reflected, returns would be less than those shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table indicate the risks and volatility of an investment in the fund by showing how the fund has performed in the past. The bar chart shows changes in the performance of the fund's Class A shares from calendar year to calendar year. The table shows the average annual total returns for each class of the fund over time and compares these returns to the returns of the Standard & Poor's 500 Index and the Russell 1000 Growth Index, each a broad-based measure of market performance that has characteristics relevant to the fund's investment strategies.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table shows the average annual total returns for each class of the fund over time and compares these returns to the returns of the Standard & Poor's 500 Index and the Russell 1000 Growth Index, each a broad-based measure of market performance that has characteristics relevant to the fund's investment strategies.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-800-225-6292
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	https://us.pioneerinvestments.com/performance
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	ANNUAL RETURN CLASS A SHARES (%) (Year ended December 31)
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The bar chart does not reflect any sales charge you may pay when you buy fund shares. If this amount was reflected, returns would be less than those shown.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	For the period covered by the bar chart: THE HIGHEST CALENDAR QUARTERLY RETURN WAS 16.34% (01/01/2012 TO 03/31/2012). THE LOWEST CALENDAR QUARTERLY RETURN WAS -21.95% (10/01/2008 TO 12/31/2008).
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURN (%) (for periods ended December 31, 2013)
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	The performance of Class A, Class B and Class C shares of the fund is the net asset value performance of the predecessor fund's shares prior to the reorganization, restated to reflect differences in any applicable sales charges and Rule 12b-1 fees (but not other differences in expenses).
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	Actual after-tax returns depend on the investor's tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are shown only for Class A shares. After-tax returns for Class B, Class C, Class R and Class Y shares will vary.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor's tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts. After-tax returns are shown only for Class A shares. After-tax returns for Class B, Class C, Class R and Class Y shares will vary.
Pioneer Oak Ridge Large Cap Growth Fund | CLASS A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.54%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.54%
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.34%)	[1]
Net Expenses	rr_NetExpensesOverAssets	1.20%	[1]
1	rr_ExpenseExampleYear01	690
3	rr_ExpenseExampleYear03	1,002
5	rr_ExpenseExampleYear05	1,336
10	rr_ExpenseExampleYear10	2,277
1	rr_ExpenseExampleNoRedemptionYear01	690
3	rr_ExpenseExampleNoRedemptionYear03	1,002
5	rr_ExpenseExampleNoRedemptionYear05	1,336
10	rr_ExpenseExampleNoRedemptionYear10	2,277
2004	rr_AnnualReturn2004	11.40%
2005	rr_AnnualReturn2005	7.57%
2006	rr_AnnualReturn2006	2.61%
2007	rr_AnnualReturn2007	7.61%
2008	rr_AnnualReturn2008	(38.29%)
2009	rr_AnnualReturn2009	33.58%
2010	rr_AnnualReturn2010	7.74%
2011	rr_AnnualReturn2011	(1.49%)
2012	rr_AnnualReturn2012	11.82%
2013	rr_AnnualReturn2013	33.36%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	HIGHEST CALENDAR QUARTERLY RETURN
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2012
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	16.34%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	LOWEST CALENDAR QUARTERLY RETURN
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(21.95%)
1 YEAR	rr_AverageAnnualReturnYear01	25.72%
5 YEARS	rr_AverageAnnualReturnYear05	14.79%
10 YEARS	rr_AverageAnnualReturnYear10	4.99%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	3.50%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Mar. 01, 1999
Pioneer Oak Ridge Large Cap Growth Fund | CLASS B
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	4.00%
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.95%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.70%
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.60%)	[1]
Net Expenses	rr_NetExpensesOverAssets	2.10%	[1]
1	rr_ExpenseExampleYear01	613
3	rr_ExpenseExampleYear03	1,082
5	rr_ExpenseExampleYear05	1,477
10	rr_ExpenseExampleYear10	2,706
1	rr_ExpenseExampleNoRedemptionYear01	213
3	rr_ExpenseExampleNoRedemptionYear03	782
5	rr_ExpenseExampleNoRedemptionYear05	1,377
10	rr_ExpenseExampleNoRedemptionYear10	2,706
1 YEAR	rr_AverageAnnualReturnYear01	28.15%
5 YEARS	rr_AverageAnnualReturnYear05	15.12%
10 YEARS	rr_AverageAnnualReturnYear10
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	4.38%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Feb. 17, 2004
Pioneer Oak Ridge Large Cap Growth Fund | CLASS C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.49%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.24%
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.14%)	[1]
Net Expenses	rr_NetExpensesOverAssets	2.10%	[1]
1	rr_ExpenseExampleYear01	313
3	rr_ExpenseExampleYear03	687
5	rr_ExpenseExampleYear05	1,187
10	rr_ExpenseExampleYear10	2,564
1	rr_ExpenseExampleNoRedemptionYear01	213
3	rr_ExpenseExampleNoRedemptionYear03	687
5	rr_ExpenseExampleNoRedemptionYear05	1,187
10	rr_ExpenseExampleNoRedemptionYear10	2,564
1 YEAR	rr_AverageAnnualReturnYear01	32.21%
5 YEARS	rr_AverageAnnualReturnYear05	15.12%
10 YEARS	rr_AverageAnnualReturnYear10
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	4.44%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Feb. 17, 2004
Pioneer Oak Ridge Large Cap Growth Fund | CLASS R
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other Expenses	rr_OtherExpensesOverAssets	0.59%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.84%
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.39%)	[1]
Net Expenses	rr_NetExpensesOverAssets	1.45%	[1]
1	rr_ExpenseExampleYear01	148
3	rr_ExpenseExampleYear03	541
5	rr_ExpenseExampleYear05	959
10	rr_ExpenseExampleYear10	2,127
1	rr_ExpenseExampleNoRedemptionYear01	148
3	rr_ExpenseExampleNoRedemptionYear03	541
5	rr_ExpenseExampleNoRedemptionYear05	959
10	rr_ExpenseExampleNoRedemptionYear10	2,127
1 YEAR	rr_AverageAnnualReturnYear01	33.02%
5 YEARS	rr_AverageAnnualReturnYear05	15.86%
10 YEARS	rr_AverageAnnualReturnYear10
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	4.91%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Feb. 17, 2004
Pioneer Oak Ridge Large Cap Growth Fund | CLASS Y
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.42%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.17%
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[1]
Net Expenses	rr_NetExpensesOverAssets	1.17%	[1]
1	rr_ExpenseExampleYear01	119
3	rr_ExpenseExampleYear03	372
5	rr_ExpenseExampleYear05	644
10	rr_ExpenseExampleYear10	1,420
1	rr_ExpenseExampleNoRedemptionYear01	119
3	rr_ExpenseExampleNoRedemptionYear03	372
5	rr_ExpenseExampleNoRedemptionYear05	644
10	rr_ExpenseExampleNoRedemptionYear10	$ 1,420
1 YEAR	rr_AverageAnnualReturnYear01	33.31%
5 YEARS	rr_AverageAnnualReturnYear05	16.36%
10 YEARS	rr_AverageAnnualReturnYear10
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	6.47%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Aug. 10, 2004
Pioneer Oak Ridge Large Cap Growth Fund | Return after taxes on distributions | CLASS A
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	25.72%
5 YEARS	rr_AverageAnnualReturnYear05	14.79%
10 YEARS	rr_AverageAnnualReturnYear10	4.81%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	3.30%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Mar. 01, 1999
Pioneer Oak Ridge Large Cap Growth Fund | Return after taxes on distributions and sale of shares | CLASS A
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	14.56%
5 YEARS	rr_AverageAnnualReturnYear05	11.93%
10 YEARS	rr_AverageAnnualReturnYear10	4.02%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	2.81%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Mar. 01, 1999
Pioneer Oak Ridge Large Cap Growth Fund | Standard & Poor’s 500 Index (reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	32.39%
5 YEARS	rr_AverageAnnualReturnYear05	17.94%
10 YEARS	rr_AverageAnnualReturnYear10	7.41%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	4.68%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Mar. 01, 1999
Pioneer Oak Ridge Large Cap Growth Fund | Russell 1000 Growth Index (reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	33.48%
5 YEARS	rr_AverageAnnualReturnYear05	20.39%
10 YEARS	rr_AverageAnnualReturnYear10	7.83%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	3.29%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Mar. 01, 1999

[1] The fund's investment adviser has contractually agreed to limit ordinary operating expenses (ordinary operating expenses means all fund expenses other than extraordinary expenses, such as litigation, taxes, brokerage commissions and acquired fund fees and expenses) to the extent required to reduce fund expenses to 1.20%, 2.10%, 2.10% and 1.45% of the average daily net assets attributable to Class A, Class B, Class C and Class R shares, respectively. These expense limitations are in effect through April 1, 2015. There can be no assurance that the adviser will extend the expense limitations beyond such times. Net expenses for a class may exceed the applicable expense limitation to the extent that the fund incurs excluded expenses. While in effect, an arrangement may be terminated for a class only by agreement of the adviser and the Board of Trustees.

XML

Pioneer Oak Ridge Large Cap Growth Fund

PIONEER OAK RIDGE LARGE CAP GROWTH FUND

INVESTMENT OBJECTIVE

Capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold shares of the fund.

You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Pioneer funds. More information about these and other discounts is available from your investment professional and in the "Sales charges" section of the prospectus beginning on page 36 and the "Sales charges" section of the statement of additional information beginning on page 53.

SHAREOWNER FEES
(fees paid directly from your investment)

Shareholder Fees Pioneer Oak Ridge Large Cap Growth Fund	CLASS A	CLASS B	CLASS C	CLASS R	CLASS Y
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	5.75%	none	none	none	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	none	4.00%	1.00%	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a
percentage of the value of your investment)

Annual Fund Operating Expenses Pioneer Oak Ridge Large Cap Growth Fund		CLASS A	CLASS B	CLASS C	CLASS R	CLASS Y
Management Fees		0.75%	0.75%	0.75%	0.75%	0.75%
Distribution and Service (12b-1) Fees		0.25%	1.00%	1.00%	0.50%	none
Other Expenses		0.54%	0.95%	0.49%	0.59%	0.42%
Total Annual Fund Operating Expenses		1.54%	2.70%	2.24%	1.84%	1.17%
Less: Fee Waiver and Expense Reimbursement	[1]	(0.34%)	(0.60%)	(0.14%)	(0.39%)	none
Net Expenses	[1]	1.20%	2.10%	2.10%	1.45%	1.17%

EXAMPLE

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the fund for the time periods shown and then, except as indicated, redeem all of your shares at the end of those periods. It also assumes that (a) your investment has a 5% return each year and (b) the fund's total annual operating expenses remain the same except for year one (which considers the effect of the expense limitation). Although your actual costs may be higher or lower, based on these assumptions your costs would be:

IF YOU REDEEM YOUR SHARES
NUMBER OF YEARS YOU OWN YOUR SHARES

Expense Example Pioneer Oak Ridge Large Cap Growth Fund (USD $)	1	3	5	10
Class A	690	1,002	1,336	2,277
Class B	613	1,082	1,477	2,706
Class C	313	687	1,187	2,564
Class R	148	541	959	2,127
Class Y	119	372	644	1,420

IF YOU DO NOT REDEEM YOUR SHARES
NUMBER OF YEARS YOU OWN YOUR SHARES

Expense Example, No Redemption Pioneer Oak Ridge Large Cap Growth Fund (USD $)	1	3	5	10
Class A	690	1,002	1,336	2,277
Class B	213	782	1,377	2,706
Class C	213	687	1,187	2,564
Class R	148	541	959	2,127
Class Y	119	372	644	1,420

PORTFOLIO TURNOVER

The fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 16% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

Normally, the fund invests at least 80% of its net assets (plus the amount of borrowings, if any, for investment purposes) in equity securities of large capitalization companies. Large capitalization companies have market capitalizations at the time of acquisition of $3 billion or more. The fund anticipates that the average weighted market capitalization of the companies in the fund's portfolio will be significantly higher than $3 billion. The equity securities in which the fund principally invests are common stocks, preferred stocks and depositary receipts, but the fund may invest in other types of equity securities to a lesser extent, such as exchange-traded funds (ETFs) that invest primarily in equity securities, equity interests in real estate investment trusts (REITs), warrants and rights. The fund may invest in initial public offerings of equity securities.

The fund may invest up to 20% of its total assets in equity and debt securities of non-U.S. issuers. The fund will not invest more than 10% of its total assets in the securities of emerging markets issuers.

The fund may invest in debt securities. The fund may invest up to 5% of its net assets in below investment grade debt securities (known as "junk bonds"), including below investment grade convertible debt securities and securities of issuers that are in default.

The fund may, but is not required to, use derivatives, such as stock index futures and options. The fund may use derivatives for a variety of purposes, including; in an attempt to hedge against adverse changes in the market prices of securities, interest rates or currency exchange rates; as a substitute for purchasing or selling securities; to attempt to increase the fund's return as a non-hedging strategy that may be considered speculative; and to manage portfolio characteristics. The fund may choose not to make use of derivatives for a variety of reasons, and any use may be limited by applicable law and regulations. The fund may also hold cash or other short-term instruments.

The fund uses a "growth" style of management and seeks to invest in issuers with above average potential for earnings growth.

When making purchase decisions for the fund, the subadviser uses a disciplined approach that involves three primary components:

• Research - The subadviser analyzes research on potential investments from a wide variety of sources, including internally generated analysis and research provided by institutions and the brokerage community.
• Fundamentals - Once a potential investment is identified, the subadviser considers whether the issuer possesses certain attributes that the subadviser believes a "buy" candidate should possess.
• Valuation - Finally, the subadviser values companies by considering price-to sales ratios and price-to-earnings ratios within a peer group.

From this process, the subadviser constructs a list of securities for the fund to purchase.

The subadviser makes sell decisions for the fund based on a number of factors, including deterioration in a company's underlying fundamentals and better relative value in other securities.

PRINCIPAL RISKS OF INVESTING IN THE FUND

You could lose money on your investment in the fund. As with any mutual fund, there is no guarantee that the fund will achieve its objective.

MARKET RISK. The values of securities held by the fund may go up or down, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic, political, or regulatory conditions, inflation, changes in interest or currency rates, lack of liquidity in the bond markets or adverse investor sentiment. Adverse market conditions may be prolonged and may not have the same impact on all types of securities. The values of securities may fall due to factors affecting a particular issuer, industry or the securities market as a whole. The stock market may perform poorly relative to other investments (this risk may be greater in the short term). High public debt in the U.S. and other countries creates ongoing and systemic market risks and policymaking uncertainty. The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities worldwide. Governmental and non-governmental issuers have defaulted on, or been forced to restructure, their debts, and many other issuers have faced difficulties obtaining credit. These market conditions may continue, worsen or spread, including in the U.S., Europe and beyond. Further defaults or restructurings by governments and others of their debt could have additional adverse effects on economies, financial markets and asset valuations around the world. In response to the crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support financial markets, including by keeping interest rates at historically low levels. More recently, the Federal Reserve has reduced its market support activities. Further reduction or withdrawal of this support, failure of efforts in response to the crisis, or investor perception that these efforts are not succeeding could negatively affect financial markets generally as well as increase market volatility and reduce the value and liquidity of certain securities. Whether or not the fund invests in securities of issuers located in or with significant exposure to countries experiencing economic and financial difficulties, the value and liquidity of the fund's investments may be negatively affected. In addition, policy and legislative changes in the U.S. and in other countries are affecting many aspects of financial regulation. The impact of these changes on the markets, and the practical implications for market participants, may not be fully known for some time. The fund may experience a substantial or complete loss on any individual security or derivative position.

GROWTH STYLE RISK. The fund's investments may not have the growth potential originally expected. Growth stocks may fall out of favor with investors and underperform the overall equity market.

PORTFOLIO SELECTION RISK. The subadviser's judgment about a particular security or issuer, or about the economy or a particular sector, region or market segment, or about an investment strategy, may prove to be incorrect.

RISKS OF NON-U.S. INVESTMENTS. Investing in non-U.S. issuers, or in U.S. issuers that have significant exposure to foreign markets, may involve unique risks compared to investing in securities of U.S. issuers. These risks are more pronounced for issuers in emerging markets or to the extent that the fund invests significantly in one region or country. These risks may include different financial reporting practices and regulatory standards, less liquid trading markets, extreme price volatility, currency risks, changes in economic, political, regulatory and social conditions, sustained economic downturns, financial instability, tax burdens, and investment and repatriation restrictions. Lack of information and less market regulation also may affect the value of these securities. Withholding and other non-U.S. taxes may decrease the fund's return. Non-U.S. issuers may be located in parts of the world that have historically been prone to natural disasters. Investing in depositary receipts is subject to many of the same risks as investing directly in non-U.S. issuers. Depositary receipts may involve higher expenses and may trade at a discount (or premium) to the underlying security.

RISKS OF INVESTMENTS IN REITS. Investments in real estate securities are affected by economic conditions, interest rates, governmental actions and other factors. In addition, investing in REITs involves unique risks. They are significantly affected by the market for real estate and are dependent upon management skills and cash flow. REITs may have lower trading volumes and may be subject to more abrupt or erratic price movements than the overall securities markets. Mortgage REITs are particularly subject to interest rate and credit risks. In addition to its own expenses, the fund will indirectly bear its proportionate share of any management and other expenses paid by REITs in which it invests. Many real estate companies, including REITs, utilize leverage.

RISKS OF WARRANTS AND RIGHTS. If the price of the underlying stock does not rise above the exercise price before the warrant expires, the warrant generally expires without any value and the fund loses any amount it paid for the warrant. The failure to exercise subscription rights to purchase common shares would result in the dilution of the fund's interest in the issuing company.

RISKS OF CONVERTIBLE SECURITIES. The market values of convertible securities tend to decline as interest rates increase and, conversely, to increase as interest rates decline. A downturn in equity markets may cause the price of convertible securities to decrease relative to other fixed income securities.

DEBT SECURITIES RISK. Factors that could contribute to a decline in the market value of debt securities in the fund include rising interest rates, if the issuer or other obligor of a security held by the fund fails to pay principal and/or interest, otherwise defaults or has its credit rating downgraded or is perceived to be less creditworthy or the credit quality or value of any underlying assets declines. Junk bonds involve greater risk of loss, are subject to greater price volatility and are less liquid, especially during periods of economic uncertainty or change, than higher quality debt securities; they may also be more difficult to value. Junk bonds have a higher risk of default or are already in default and are considered speculative.

MARKET SEGMENT RISK. To the extent the fund emphasizes, from time to time, investments in a market segment, the fund will be subject to a greater degree to the risks particular to that segment, and may experience greater market fluctuation than a fund without the same focus.

DERIVATIVES RISK. Using stock index futures and options and other derivatives can increase fund losses and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves behave in a way not anticipated by the fund. Using derivatives may increase the volatility of the fund's net asset value and may not provide the result intended. Derivatives may have a leveraging effect on the fund. Some derivatives have the potential for unlimited loss, regardless of the size of the fund's initial investment. Changes in a derivative's value may not correlate well with the referenced asset or metric. The fund also may have to sell assets at inopportune times to satisfy its obligations. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. New regulations are changing the derivatives markets. The regulations may make using derivatives more costly, may limit their availability, or may otherwise adversely affect their value or performance. For derivatives that are required to be traded through a clearinghouse or exchange, the fund also will be exposed to the credit risk of the clearinghouse and the broker that submits trades for the fund. It is possible that certain derivatives that are required to be cleared, such as certain swap contracts, will not be accepted for clearing. In addition, regulated trading facilities for swap contracts are relatively new; they may not function as intended, which could impair the ability to enter into swap contracts. The extent and impact of the new regulations are not yet fully known and may not be for some time.

RISKS OF INITIAL PUBLIC OFFERINGS. Companies involved in initial public offerings (IPOs) generally have limited operating histories, and prospects for future profitability are uncertain. Information about the companies may be available for very limited periods. The market for IPO issuers has been volatile, and share prices of newly public companies have fluctuated significantly over short periods of time. Further, stocks of newly-public companies may decline shortly after the IPO. There is no assurance that the fund will have access to IPOs. The purchase of IPO shares may involve high transaction costs.

RISKS OF INVESTMENT IN OTHER FUNDS. Investing in other investment companies, including exchange-traded funds (ETFs), subjects the fund to the risks of investing in the underlying securities or assets held by those funds. When investing in another fund, the fund will bear a pro rata portion of the underlying fund's expenses, in addition to its own expenses.

LEVERAGING RISK. The value of your investment may be more volatile and other risks tend to be compounded if the fund borrows or uses derivatives or other investments, such as ETFs, that have embedded leverage. Leverage generally magnifies the effect of any increase or decrease in the value of the fund's underlying assets or creates investment risk with respect to a larger pool of assets than the fund would otherwise have, potentially resulting in the loss of all assets. Engaging in such transactions may cause the fund to liquidate positions when it may not be advantageous to do so to satisfy its obligations or meet segregation requirements.

EXPENSE RISK. Your actual costs of investing in the fund may be higher than the expenses shown in "Annual fund operating expenses" for a variety of reasons. For example, expense ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile.

Please note that there are many other factors that could adversely affect your investment and that could prevent the fund from achieving its goals.

An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

THE FUND'S PAST PERFORMANCE

The bar chart and table indicate the risks and volatility of an investment in the fund by showing how the fund has performed in the past. The bar chart shows changes in the performance of the fund's Class A shares from calendar year to calendar year. The table shows the average annual total returns for each class of the fund over time and compares these returns to the returns of the Standard & Poor's 500 Index and the Russell 1000 Growth Index, each a broad-based measure of market performance that has characteristics relevant to the fund's investment strategies. You can obtain updated performance information by visiting https://us.pioneerinvestments.com/performance or by calling 1-800-225-6292.

The fund acquired the assets and liabilities of Oak Ridge Large Cap Equity Fund (the predecessor fund) on February 13, 2004. As a result of the reorganization, the fund is the accounting successor of the predecessor fund.

In the reorganization, the predecessor fund exchanged its assets for Class A shares of the fund. The performance of Class A, Class B and Class C shares of the fund is the net asset value performance of the predecessor fund's shares prior to the reorganization, restated to reflect differences in any applicable sales charges and Rule 12b-1 fees (but not other differences in expenses). This adjustment had the effect of reducing the previously reported performance of the predecessor fund.

The fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

The bar chart does not reflect any sales charge you may pay when you buy fund shares. If this amount was reflected, returns would be less than those shown.

ANNUAL RETURN CLASS A SHARES (%)

(Year ended December 31)

For the period covered by the bar chart:
THE HIGHEST CALENDAR QUARTERLY RETURN WAS 16.34% (01/01/2012 TO 03/31/2012).
THE LOWEST CALENDAR QUARTERLY RETURN WAS -21.95% (10/01/2008 TO 12/31/2008).

AVERAGE ANNUAL TOTAL RETURN (%)

(for periods ended December 31, 2013)

Average Annual Total Returns Pioneer Oak Ridge Large Cap Growth Fund	1 YEAR	5 YEARS	10 YEARS	SINCE INCEPTION	INCEPTION DATE
Class A	25.72%	14.79%	4.99%	3.50%	Mar. 01, 1999
Class A Return after taxes on distributions	25.72%	14.79%	4.81%	3.30%	Mar. 01, 1999
Class A Return after taxes on distributions and sale of shares	14.56%	11.93%	4.02%	2.81%	Mar. 01, 1999
Class B	28.15%	15.12%		4.38%	Feb. 17, 2004
Class C	32.21%	15.12%		4.44%	Feb. 17, 2004
Class R	33.02%	15.86%		4.91%	Feb. 17, 2004
Class Y	33.31%	16.36%		6.47%	Aug. 10, 2004
Standard & Poor’s 500 Index (reflects no deduction for fees, expenses or taxes)	32.39%	17.94%	7.41%	4.68%	Mar. 01, 1999
Russell 1000 Growth Index (reflects no deduction for fees, expenses or taxes)	33.48%	20.39%	7.83%	3.29%	Mar. 01, 1999

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor's tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.

After-tax returns are shown only for Class A shares. After-tax returns for Class B, Class C, Class R and Class Y shares will vary.

[1] The fund's investment adviser has contractually agreed to limit ordinary operating expenses (ordinary operating expenses means all fund expenses other than extraordinary expenses, such as litigation, taxes, brokerage commissions and acquired fund fees and expenses) to the extent required to reduce fund expenses to 1.20%, 2.10%, 2.10% and 1.45% of the average daily net assets attributable to Class A, Class B, Class C and Class R shares, respectively. These expense limitations are in effect through April 1, 2015. There can be no assurance that the adviser will extend the expense limitations beyond such times. Net expenses for a class may exceed the applicable expense limitation to the extent that the fund incurs excluded expenses. While in effect, an arrangement may be terminated for a class only by agreement of the adviser and the Board of Trustees.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	PIONEER SERIES TRUST I
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Pioneer Oak Ridge Small Cap Growth Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	PIONEER OAK RIDGE SMALL CAP GROWTH FUND
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Capital appreciation.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the fund. You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Pioneer funds. More information about these and other discounts is available from your investment professional and in the "Sales charges" section of the prospectus beginning on page 37 and the "Sales charges" section of the statement of additional information beginning on page 53.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	SHAREOWNER FEES (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	PORTFOLIO TURNOVER
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 24% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	24.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Pioneer funds.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the fund for the time periods shown and then, except as indicated, redeem all of your shares at the end of those periods. It also assumes that (a) your investment has a 5% return each year and (b) the fund's total annual operating expenses remain the same except for year one (which considers the effect of the expense limitation). Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example by, Year, Caption [Text]	rr_ExpenseExampleByYearCaption	IF YOU REDEEM YOUR SHARES NUMBER OF YEARS YOU OWN YOUR SHARES
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	IF YOU DO NOT REDEEM YOUR SHARES NUMBER OF YEARS YOU OWN YOUR SHARES
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Normally, the fund invests at least 80% of its net assets (plus the amount of borrowings, if any, for investment purposes) in equity securities of small capitalization companies. Small capitalization companies are those with market values, at the time of investment, that do not exceed the greater of the market capitalization of the largest company within the Russell 2000 Index ($5.27 billion as of December 31, 2013) or the 3-year rolling average of the market capitalization of the largest company within the Russell 2000 Index ($4.54 billion as of December 31, 2013) as measured at the end of the preceding month. The Russell 2000 Index is comprised of the 2,000 smallest U.S. domiciled, publicly traded stocks that are included in the Russell 3000 Index. The size of the companies in the Index changes constantly as a result of market conditions and the composition of the Index. The fund's investments will not be confined to securities issued by companies included in the Index. For purposes of the fund's investment policies, equity securities include common stocks and other equity instruments, such as exchange-traded funds (ETFs) that invest primarily in equity securities, depositary receipts, warrants, rights, equity investments in real estate investment trusts (REITs) and preferred stocks. The fund may invest in initial public offerings of equity securities. The fund may invest up to 20% of its total assets in equity and debt securities of non-U.S. issuers. The fund will not invest more than 10% of its total assets in the securities of emerging markets issuers. The fund may invest in debt securities. The fund may invest up to 5% of its net assets in below investment grade debt securities (known as "junk bonds"), including below investment grade convertible debt securities and securities of issuers that are in default. The fund may, but is not required to, use derivatives, such as stock index futures and options. The fund may use derivatives for a variety of purposes, including: in an attempt to hedge against adverse changes in the market prices of securities, interest rates or currency exchange rates; as a substitute for purchasing or selling securities; to attempt to increase the fund's return as a non-hedging strategy that may be considered speculative; and to manage portfolio characteristics. The fund may choose not to make use of derivatives for a variety of reasons, and any use may be limited by applicable law and regulations. The fund may also hold cash or other short-term instruments. The fund uses a "growth" style of management and seeks to invest in issuers with above average potential for earnings growth. When making purchase decisions for the fund, the subadviser uses a disciplined approach that involves three primary components: Research - The subadviser analyzes research on potential investments from a wide variety of sources, including internally generated analysis and research provided by institutions and the brokerage community. Fundamentals - Once a potential investment is identified, the subadviser considers whether the issuer possesses certain attributes that the subadviser believes a "buy" candidate should possess. Valuation - Finally, the subadviser values companies by considering price-to sales ratios and price-to-earnings ratios within a peer group. From this process, the subadviser constructs a list of securities for the fund to purchase. The subadviser makes sell decisions for the fund based on a number of factors, including deterioration in a company's underlying fundamentals and better relative value in other securities.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS OF INVESTING IN THE FUND
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	You could lose money on your investment in the fund. As with any mutual fund, there is no guarantee that the fund will achieve its objective. MARKET RISK. The values of securities held by the fund may go up or down, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic, political, or regulatory conditions, inflation, changes in interest or currency rates, lack of liquidity in the bond markets or adverse investor sentiment. Adverse market conditions may be prolonged and may not have the same impact on all types of securities. The values of securities may fall due to factors affecting a particular issuer, industry or the securities market as a whole. The stock market may perform poorly relative to other investments (this risk may be greater in the short term). High public debt in the U.S. and other countries creates ongoing and systemic market risks and policymaking uncertainty. The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities worldwide. Governmental and non-governmental issuers have defaulted on, or been forced to restructure, their debts, and many other issuers have faced difficulties obtaining credit. These market conditions may continue, worsen or spread, including in the U.S., Europe and beyond. Further defaults or restructurings by governments and others of their debt could have additional adverse effects on economies, financial markets and asset valuations around the world. In response to the crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support financial markets, including by keeping interest rates at historically low levels. More recently, the Federal Reserve has reduced its market support activities. Further reduction or withdrawal of this support, failure of efforts in response to the crisis, or investor perception that these efforts are not succeeding could negatively affect financial markets generally as well as increase market volatility and reduce the value and liquidity of certain securities. Whether or not the fund invests in securities of issuers located in or with significant exposure to countries experiencing economic and financial difficulties, the value and liquidity of the fund's investments may be negatively affected. In addition, policy and legislative changes in the U.S. and in other countries are affecting many aspects of financial regulation. The impact of these changes on the markets, and the practical implications for market participants, may not be fully known for some time. The fund may experience a substantial or complete loss on any individual security or derivative position. SMALL-SIZE COMPANIES RISK. Compared to large companies, small-size companies, and the market for their equity securities, may be more sensitive to changes in earnings results and investor expectations, have more limited product lines and capital resources, experience sharper swings in market values, have limited liquidity, be harder to value or to sell at the times and prices the subadviser thinks appropriate, and offer greater potential for gain and loss. GROWTH STYLE RISK. The fund's investments may not have the growth potential originally expected. Growth stocks may fall out of favor with investors and underperform the overall equity market. PORTFOLIO SELECTION RISK. The subadviser's judgment about a particular security or issuer, or about the economy or a particular sector, region or market segment, or about an investment strategy, may prove to be incorrect. RISKS OF NON-U.S. INVESTMENTS. Investing in non-U.S. issuers, or in U.S. issuers that have significant exposure to foreign markets, may involve unique risks compared to investing in securities of U.S. issuers. These risks are more pronounced for issuers in emerging markets or to the extent that the fund invests significantly in one region or country. These risks may include different financial reporting practices and regulatory standards, less liquid trading markets, extreme price volatility, currency risks, changes in economic, political, regulatory and social conditions, sustained economic downturns, financial instability, tax burdens, and investment and repatriation restrictions. Lack of information and less market regulation also may affect the value of these securities. Withholding and other non-U.S. taxes may decrease the fund's return. Non-U.S. issuers may be located in parts of the world that have historically been prone to natural disasters. Investing in depositary receipts is subject to many of the same risks as investing directly in non-U.S. issuers. Depositary receipts may involve higher expenses and may trade at a discount (or premium) to the underlying security. RISKS OF INVESTMENTS IN REITS. Investments in real estate securities are affected by economic conditions, interest rates, governmental actions and other factors. In addition, investing in REITs involves unique risks. They are significantly affected by the market for real estate and are dependent upon management skills and cash flow. REITs may have lower trading volumes and may be subject to more abrupt or erratic price movements than the overall securities markets. Mortgage REITs are particularly subject to interest rate and credit risks. In addition to its own expenses, the fund will indirectly bear its proportionate share of any management and other expenses paid by REITs in which it invests. Many real estate companies, including REITs, utilize leverage. RISKS OF WARRANTS AND RIGHTS. If the price of the underlying stock does not rise above the exercise price before the warrant expires, the warrant generally expires without any value and the fund loses any amount it paid for the warrant. The failure to exercise subscription rights to purchase common shares would result in the dilution of the fund's interest in the issuing company. PREFERRED STOCKS RISK. Preferred stocks may pay fixed or adjustable rates of return. Preferred stocks are subject to issuer-specific and market risks applicable generally to equity securities. In addition, a company's preferred stocks generally pay dividends only after the company makes required payments to holders of its bonds and other debt. Thus, the value of preferred stocks will usually react more strongly than bonds and other debt to actual or perceived changes in the company's financial condition or prospects. The market value of preferred stocks generally decreases when interest rates rise. Preferred stocks of smaller companies may be more vulnerable to adverse developments than preferred stocks of larger companies. RISKS OF CONVERTIBLE SECURITIES. The market values of convertible securities tend to decline as interest rates increase and, conversely, to increase as interest rates decline. A downturn in equity markets may cause the price of convertible securities to decrease relative to other fixed income securities. DEBT SECURITIES RISK. Factors that could contribute to a decline in the market value of debt securities in the fund include rising interest rates, if the issuer or other obligor of a security held by the fund fails to pay principal and/or interest, otherwise defaults or has its credit rating downgraded or is perceived to be less creditworthy or the credit quality or value of any underlying assets declines. Junk bonds involve greater risk of loss, are subject to greater price volatility and are less liquid, especially during periods of economic uncertainty or change, than higher quality debt securities; they may also be more difficult to value. Junk bonds have a higher risk of default or are already in default and are considered speculative. MARKET SEGMENT RISK. To the extent the fund emphasizes, from time to time, investments in a market segment, the fund will be subject to a greater degree to the risks particular to that segment, and may experience greater market fluctuation than a fund without the same focus. DERIVATIVES RISK. Using stock index futures and options and other derivatives can increase fund losses and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves behave in a way not anticipated by the fund. Using derivatives may increase the volatility of the fund's net asset value and may not provide the result intended. Derivatives may have a leveraging effect on the fund. Some derivatives have the potential for unlimited loss, regardless of the size of the fund's initial investment. Changes in a derivative's value may not correlate well with the referenced asset or metric. The fund also may have to sell assets at inopportune times to satisfy its obligations. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. New regulations are changing the derivatives markets. The regulations may make using derivatives more costly, may limit their availability, or may otherwise adversely affect their value or performance. For derivatives that are required to be traded through a clearinghouse or exchange, the fund also will be exposed to the credit risk of the clearinghouse and the broker that submits trades for the fund. It is possible that certain derivatives that are required to be cleared, such as certain swap contracts, will not be accepted for clearing. In addition, regulated trading facilities for swap contracts are relatively new; they may not function as intended, which could impair the ability to enter into swap contracts. The extent and impact of the new regulations are not yet fully known and may not be for some time. RISKS OF INITIAL PUBLIC OFFERINGS. Companies involved in initial public offerings (IPOs) generally have limited operating histories, and prospects for future profitability are uncertain. Information about the companies may be available for very limited periods. The market for IPO issuers has been volatile, and share prices of newly public companies have fluctuated significantly over short periods of time. Further, stocks of newly-public companies may decline shortly after the IPO. There is no assurance that the fund will have access to IPOs. The purchase of IPO shares may involve high transaction costs. RISKS OF INVESTMENT IN OTHER FUNDS. Investing in other investment companies, including exchange-traded funds (ETFs), subjects the fund to the risks of investing in the underlying securities or assets held by those funds. When investing in another fund, the fund will bear a pro rata portion of the underlying fund's expenses, in addition to its own expenses. LEVERAGING RISK. The value of your investment may be more volatile and other risks tend to be compounded if the fund borrows or uses derivatives or other investments, such as ETFs, that have embedded leverage. Leverage generally magnifies the effect of any increase or decrease in the value of the fund's underlying assets or creates investment risk with respect to a larger pool of assets than the fund would otherwise have, potentially resulting in the loss of all assets. Engaging in such transactions may cause the fund to liquidate positions when it may not be advantageous to do so to satisfy its obligations or meet segregation requirements. EXPENSE RISK. Your actual costs of investing in the fund may be higher than the expenses shown in "Annual fund operating expenses" for a variety of reasons. For example, expense ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile. Please note that there are many other factors that could adversely affect your investment and that could prevent the fund from achieving its goals. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text]	rr_RiskLoseMoney	You could lose money on your investment in the fund.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	THE FUND'S PAST PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table indicate the risks and volatility of an investment in the fund by showing how the fund has performed in the past. The bar chart shows changes in the performance of the fund's Class A shares from calendar year to calendar year. The table shows the average annual total returns for each class of the fund over time and compares these returns to the returns of the Russell 2000 Index and the Russell 2000 Growth Index, each a broad-based measure of market performance that has characteristics relevant to the fund's investment strategies. You can obtain updated performance information by visiting https://us.pioneerinvestments.com/performance or by calling 1-800-225-6292. The fund acquired the assets and liabilities of Oak Ridge Small Cap Equity Fund (the predecessor fund) on February 13, 2004. As a result of the reorganization, the fund is the accounting successor of the predecessor fund. In the reorganization, the predecessor fund exchanged its assets for Class A and Class C shares of the fund. The performance of Class A, Class B and Class C shares of the fund is the net asset value performance of the predecessor fund's Class A shares (Class C shares in the case of the fund's Class C shares) prior to the reorganization, restated to reflect differences in any applicable sales charges and Rule 12b-1 fees (but not other differences in expenses). This adjustment had the effect of reducing the previously reported performance of the predecessor fund. The fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. The bar chart does not reflect any sales charge you may pay when you buy fund shares. If this amount was reflected, returns would be less than those shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table indicate the risks and volatility of an investment in the fund by showing how the fund has performed in the past. The bar chart shows changes in the performance of the fund's Class A shares from calendar year to calendar year. The table shows the average annual total returns for each class of the fund over time and compares these returns to the returns of the Russell 2000 Index and the Russell 2000 Growth Index, each a broad-based measure of market performance that has characteristics relevant to the fund's investment strategies.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table shows the average annual total returns for each class of the fund over time and compares these returns to the returns of the Russell 2000 Index and the Russell 2000 Growth Index, each a broad-based measure of market performance that has characteristics relevant to the fund's investment strategies.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-800-225-6292
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	https://us.pioneerinvestments.com/performance
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	ANNUAL RETURN CLASS A SHARES (%) (Year ended December 31)
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The bar chart does not reflect any sales charge you may pay when you buy fund shares. If this amount was reflected, returns would be less than those shown.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	For the period covered by the bar chart: THE HIGHEST CALENDAR QUARTERLY RETURN WAS 20.45% (04/01/2009 TO 06/30/2009). THE LOWEST CALENDAR QUARTERLY RETURN WAS -22.25% (10/01/2008  TO 12/31/2008).
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURN (%) (for periods ended December 31, 2013)
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	The performance of Class A, Class B and Class C shares of the fund is the net asset value performance of the predecessor fund's Class A shares (Class C shares in the case of the fund's Class C shares) prior to the reorganization, restated to reflect differences in any applicable sales charges and Rule 12b-1 fees (but not other differences in expenses).
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	Actual after-tax returns depend on the investor's tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are shown only for Class A shares. After-tax returns for Class B, Class C, Class K, Class R and Class Y shares will vary.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor's tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts. After-tax returns are shown only for Class A shares. After-tax returns for Class B, Class C, Class K, Class R and Class Y shares will vary.
Pioneer Oak Ridge Small Cap Growth Fund | CLASS A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fees	rr_ManagementFeesOverAssets	0.83%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.32%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.40%	[1]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[1]
Net Expenses	rr_NetExpensesOverAssets	1.40%	[1]
1	rr_ExpenseExampleYear01	709
3	rr_ExpenseExampleYear03	993
5	rr_ExpenseExampleYear05	1,297
10	rr_ExpenseExampleYear10	2,158
1	rr_ExpenseExampleNoRedemptionYear01	709
3	rr_ExpenseExampleNoRedemptionYear03	993
5	rr_ExpenseExampleNoRedemptionYear05	1,297
10	rr_ExpenseExampleNoRedemptionYear10	2,158
2004	rr_AnnualReturn2004	22.60%
2005	rr_AnnualReturn2005	6.27%
2006	rr_AnnualReturn2006	6.70%
2007	rr_AnnualReturn2007	10.38%
2008	rr_AnnualReturn2008	(29.79%)
2009	rr_AnnualReturn2009	26.08%
2010	rr_AnnualReturn2010	28.91%
2011	rr_AnnualReturn2011	0.92%
2012	rr_AnnualReturn2012	10.56%
2013	rr_AnnualReturn2013	38.99%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	HIGHEST CALENDAR QUARTERLY RETURN
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	20.45%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	LOWEST CALENDAR QUARTERLY RETURN
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(22.25%)
1 YEAR	rr_AverageAnnualReturnYear01	30.98%
5 YEARS	rr_AverageAnnualReturnYear05	18.89%
10 YEARS	rr_AverageAnnualReturnYear10	9.85%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	10.83%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Jan. 03, 1994
Pioneer Oak Ridge Small Cap Growth Fund | CLASS B
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	4.00%
Management Fees	rr_ManagementFeesOverAssets	0.83%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.65%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.48%	[1]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.18%)	[1]
Net Expenses	rr_NetExpensesOverAssets	2.30%	[1]
1	rr_ExpenseExampleYear01	633
3	rr_ExpenseExampleYear03	1,055
5	rr_ExpenseExampleYear05	1,404
10	rr_ExpenseExampleYear10	2,536
1	rr_ExpenseExampleNoRedemptionYear01	233
3	rr_ExpenseExampleNoRedemptionYear03	755
5	rr_ExpenseExampleNoRedemptionYear05	1,304
10	rr_ExpenseExampleNoRedemptionYear10	2,536
1 YEAR	rr_AverageAnnualReturnYear01	33.75%
5 YEARS	rr_AverageAnnualReturnYear05	19.23%
10 YEARS	rr_AverageAnnualReturnYear10
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	9.33%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Feb. 17, 2004
Pioneer Oak Ridge Small Cap Growth Fund | CLASS C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%
Management Fees	rr_ManagementFeesOverAssets	0.83%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.29%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.12%	[1]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[1]
Net Expenses	rr_NetExpensesOverAssets	2.12%	[1]
1	rr_ExpenseExampleYear01	315
3	rr_ExpenseExampleYear03	664
5	rr_ExpenseExampleYear05	1,139
10	rr_ExpenseExampleYear10	2,452
1	rr_ExpenseExampleNoRedemptionYear01	215
3	rr_ExpenseExampleNoRedemptionYear03	664
5	rr_ExpenseExampleNoRedemptionYear05	1,139
10	rr_ExpenseExampleNoRedemptionYear10	2,452
1 YEAR	rr_AverageAnnualReturnYear01	37.99%
5 YEARS	rr_AverageAnnualReturnYear05	19.34%
10 YEARS	rr_AverageAnnualReturnYear10	9.61%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	8.59%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Mar. 01, 1997
Pioneer Oak Ridge Small Cap Growth Fund | CLASS K
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fees	rr_ManagementFeesOverAssets	0.83%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.06%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.89%	[1]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[1]
Net Expenses	rr_NetExpensesOverAssets	0.89%	[1]
1	rr_ExpenseExampleYear01	91
3	rr_ExpenseExampleYear03	284
5	rr_ExpenseExampleYear05	493
10	rr_ExpenseExampleYear10	1,096
1	rr_ExpenseExampleNoRedemptionYear01	91
3	rr_ExpenseExampleNoRedemptionYear03	284
5	rr_ExpenseExampleNoRedemptionYear05	493
10	rr_ExpenseExampleNoRedemptionYear10	1,096
1 YEAR	rr_AverageAnnualReturnYear01	39.73%
5 YEARS	rr_AverageAnnualReturnYear05
10 YEARS	rr_AverageAnnualReturnYear10
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	37.83%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Dec. 20, 2012
Pioneer Oak Ridge Small Cap Growth Fund | CLASS R
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fees	rr_ManagementFeesOverAssets	0.83%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other Expenses	rr_OtherExpensesOverAssets	0.38%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.71%	[1]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.11%)	[1]
Net Expenses	rr_NetExpensesOverAssets	1.60%	[1]
1	rr_ExpenseExampleYear01	163
3	rr_ExpenseExampleYear03	528
5	rr_ExpenseExampleYear05	918
10	rr_ExpenseExampleYear10	2,010
1	rr_ExpenseExampleNoRedemptionYear01	163
3	rr_ExpenseExampleNoRedemptionYear03	528
5	rr_ExpenseExampleNoRedemptionYear05	918
10	rr_ExpenseExampleNoRedemptionYear10	2,010
1 YEAR	rr_AverageAnnualReturnYear01	38.77%
5 YEARS	rr_AverageAnnualReturnYear05
10 YEARS	rr_AverageAnnualReturnYear10
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	22.72%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Apr. 02, 2012
Pioneer Oak Ridge Small Cap Growth Fund | CLASS Y
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fees	rr_ManagementFeesOverAssets	0.83%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.19%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.02%	[1]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[1]
Net Expenses	rr_NetExpensesOverAssets	1.02%	[1]
1	rr_ExpenseExampleYear01	104
3	rr_ExpenseExampleYear03	325
5	rr_ExpenseExampleYear05	563
10	rr_ExpenseExampleYear10	1,248
1	rr_ExpenseExampleNoRedemptionYear01	104
3	rr_ExpenseExampleNoRedemptionYear03	325
5	rr_ExpenseExampleNoRedemptionYear05	563
10	rr_ExpenseExampleNoRedemptionYear10	$ 1,248
1 YEAR	rr_AverageAnnualReturnYear01	39.55%
5 YEARS	rr_AverageAnnualReturnYear05
10 YEARS	rr_AverageAnnualReturnYear10
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	18.91%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Dec. 29, 2009
Pioneer Oak Ridge Small Cap Growth Fund | Return after taxes on distributions | CLASS A
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	29.47%
5 YEARS	rr_AverageAnnualReturnYear05	18.33%
10 YEARS	rr_AverageAnnualReturnYear10	9.35%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	9.96%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Jan. 03, 1994
Pioneer Oak Ridge Small Cap Growth Fund | Return after taxes on distributions and sale of shares | CLASS A
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	18.72%
5 YEARS	rr_AverageAnnualReturnYear05	15.44%
10 YEARS	rr_AverageAnnualReturnYear10	8.13%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	9.12%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Jan. 03, 1994
Pioneer Oak Ridge Small Cap Growth Fund | Russell 2000 Index (reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	38.82%
5 YEARS	rr_AverageAnnualReturnYear05	20.08%
10 YEARS	rr_AverageAnnualReturnYear10	9.07%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	9.32%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Jan. 03, 1994
Pioneer Oak Ridge Small Cap Growth Fund | Russell 2000 Growth Index (reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	43.30%
5 YEARS	rr_AverageAnnualReturnYear05	22.58%
10 YEARS	rr_AverageAnnualReturnYear10	9.41%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	7.46%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Jan. 03, 1994

[1] The fund's investment adviser has contractually agreed to limit ordinary operating expenses (ordinary operating expenses means all fund expenses other than extraordinary expenses, such as litigation, taxes, brokerage commissions and acquired fund fees and expenses) to the extent required to reduce fund expenses to 2.30% and 1.60% of the average daily net assets attributable to Class B and Class R, respectively. These expense limitations are in effect through April 1, 2015. There can be no assurance that the adviser will extend the expense limitation beyond such time. Net expenses for a class may exceed the applicable expense limitation to the extent that the fund incurs excluded expenses. While in effect, an arrangement may be terminated for a class only by agreement of the adviser and the Board of Trustees.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Nov. 30, 2013
Registrant Name	dei_EntityRegistrantName	PIONEER SERIES TRUST I
Central Index Key	dei_EntityCentralIndexKey	0001257951
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Mar. 25, 2014
Document Effective Date	dei_DocumentEffectiveDate	Apr. 01, 2014
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	PIONEER SERIES TRUST I
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Document Creation Date	dei_DocumentCreationDate	Mar. 25, 2014

XML

Pioneer Oak Ridge Small Cap Growth Fund

PIONEER OAK RIDGE SMALL CAP GROWTH FUND

INVESTMENT OBJECTIVE

Capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold shares of the fund.

You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Pioneer funds. More information about these and other discounts is available from your investment professional and in the "Sales charges" section of the prospectus beginning on page 37 and the "Sales charges" section of the statement of additional information beginning on page 53.

SHAREOWNER FEES
(fees paid directly from your
investment)

Shareholder Fees Pioneer Oak Ridge Small Cap Growth Fund	CLASS A	CLASS B	CLASS C	CLASS K	CLASS R	CLASS Y
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	5.75%	none	none	none	none	none
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	none	4.00%	1.00%	none	none	none

ANNUAL FUND OPERATING
EXPENSES
(expenses that you pay each year as a
percentage of the value of your
investment)

Annual Fund Operating Expenses Pioneer Oak Ridge Small Cap Growth Fund		CLASS A	CLASS B	CLASS C	CLASS K	CLASS R	CLASS Y
Management Fees		0.83%	0.83%	0.83%	0.83%	0.83%	0.83%
Distribution and Service (12b-1) Fees		0.25%	1.00%	1.00%	none	0.50%	none
Other Expenses		0.32%	0.65%	0.29%	0.06%	0.38%	0.19%
Total Annual Fund Operating Expenses	[1]	1.40%	2.48%	2.12%	0.89%	1.71%	1.02%
Less: Fee Waiver and Expense Reimbursement	[1]	none	(0.18%)	none	none	(0.11%)	none
Net Expenses	[1]	1.40%	2.30%	2.12%	0.89%	1.60%	1.02%

EXAMPLE

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the fund for the time periods shown and then, except as indicated, redeem all of your shares at the end of those periods. It also assumes that (a) your investment has a 5% return each year and (b) the fund's total annual operating expenses remain the same except for year one (which considers the effect of the expense limitation). Although your actual costs may be higher or lower, based on these assumptions your costs would be:

IF YOU REDEEM YOUR SHARES
NUMBER OF YEARS YOU OWN YOUR SHARES

Expense Example Pioneer Oak Ridge Small Cap Growth Fund (USD $)	1	3	5	10
Class A	709	993	1,297	2,158
Class B	633	1,055	1,404	2,536
Class C	315	664	1,139	2,452
Class K	91	284	493	1,096
Class R	163	528	918	2,010
Class Y	104	325	563	1,248

IF YOU DO NOT REDEEM YOUR SHARES
NUMBER OF YEARS YOU OWN YOUR SHARES

Expense Example, No Redemption Pioneer Oak Ridge Small Cap Growth Fund (USD $)	1	3	5	10
Class A	709	993	1,297	2,158
Class B	233	755	1,304	2,536
Class C	215	664	1,139	2,452
Class K	91	284	493	1,096
Class R	163	528	918	2,010
Class Y	104	325	563	1,248

PORTFOLIO TURNOVER

The fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 24% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

Normally, the fund invests at least 80% of its net assets (plus the amount of borrowings, if any, for investment purposes) in equity securities of small capitalization companies. Small capitalization companies are those with market values, at the time of investment, that do not exceed the greater of the market capitalization of the largest company within the Russell 2000 Index ($5.27 billion as of December 31, 2013) or the 3-year rolling average of the market capitalization of the largest company within the Russell 2000 Index ($4.54 billion as of December 31, 2013) as measured at the end of the preceding month. The Russell 2000 Index is comprised of the 2,000 smallest U.S. domiciled, publicly traded stocks that are included in the Russell 3000 Index. The size of the companies in the Index changes constantly as a result of market conditions and the composition of the Index. The fund's investments will not be confined to securities issued by companies included in the Index. For purposes of the fund's investment policies, equity securities include common stocks and other equity instruments, such as exchange-traded funds (ETFs) that invest primarily in equity securities, depositary receipts, warrants, rights, equity investments in real estate investment trusts (REITs) and preferred stocks. The fund may invest in initial public offerings of equity securities.

The fund may invest up to 20% of its total assets in equity and debt securities of non-U.S. issuers. The fund will not invest more than 10% of its total assets in the securities of emerging markets issuers.

The fund may invest in debt securities. The fund may invest up to 5% of its net assets in below investment grade debt securities (known as "junk bonds"), including below investment grade convertible debt securities and securities of issuers that are in default.

The fund may, but is not required to, use derivatives, such as stock index futures and options. The fund may use derivatives for a variety of purposes, including: in an attempt to hedge against adverse changes in the market prices of securities, interest rates or currency exchange rates; as a substitute for purchasing or selling securities; to attempt to increase the fund's return as a non-hedging strategy that may be considered speculative; and to manage portfolio characteristics. The fund may choose not to make use of derivatives for a variety of reasons, and any use may be limited by applicable law and regulations. The fund may also hold cash or other short-term instruments.

The fund uses a "growth" style of management and seeks to invest in issuers with above average potential for earnings growth.

When making purchase decisions for the fund, the subadviser uses a disciplined approach that involves three primary components:

• Research - The subadviser analyzes research on potential investments from a wide variety of sources, including internally generated analysis and research provided by institutions and the brokerage community.
• Fundamentals - Once a potential investment is identified, the subadviser considers whether the issuer possesses certain attributes that the subadviser believes a "buy" candidate should possess.
• Valuation - Finally, the subadviser values companies by considering price-to sales ratios and price-to-earnings ratios within a peer group.

From this process, the subadviser constructs a list of securities for the fund to purchase.

The subadviser makes sell decisions for the fund based on a number of factors, including deterioration in a company's underlying fundamentals and better relative value in other securities.

PRINCIPAL RISKS OF INVESTING IN THE FUND

You could lose money on your investment in the fund. As with any mutual fund, there is no guarantee that the fund will achieve its objective.

MARKET RISK. The values of securities held by the fund may go up or down, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic, political, or regulatory conditions, inflation, changes in interest or currency rates, lack of liquidity in the bond markets or adverse investor sentiment. Adverse market conditions may be prolonged and may not have the same impact on all types of securities. The values of securities may fall due to factors affecting a particular issuer, industry or the securities market as a whole. The stock market may perform poorly relative to other investments (this risk may be greater in the short term). High public debt in the U.S. and other countries creates ongoing and systemic market risks and policymaking uncertainty. The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities worldwide. Governmental and non-governmental issuers have defaulted on, or been forced to restructure, their debts, and many other issuers have faced difficulties obtaining credit. These market conditions may continue, worsen or spread, including in the U.S., Europe and beyond. Further defaults or restructurings by governments and others of their debt could have additional adverse effects on economies, financial markets and asset valuations around the world. In response to the crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support financial markets, including by keeping interest rates at historically low levels. More recently, the Federal Reserve has reduced its market support activities. Further reduction or withdrawal of this support, failure of efforts in response to the crisis, or investor perception that these efforts are not succeeding could negatively affect financial markets generally as well as increase market volatility and reduce the value and liquidity of certain securities. Whether or not the fund invests in securities of issuers located in or with significant exposure to countries experiencing economic and financial difficulties, the value and liquidity of the fund's investments may be negatively affected. In addition, policy and legislative changes in the U.S. and in other countries are affecting many aspects of financial regulation. The impact of these changes on the markets, and the practical implications for market participants, may not be fully known for some time. The fund may experience a substantial or complete loss on any individual security or derivative position.

SMALL-SIZE COMPANIES RISK. Compared to large companies, small-size companies, and the market for their equity securities, may be more sensitive to changes in earnings results and investor expectations, have more limited product lines and capital resources, experience sharper swings in market values, have limited liquidity, be harder to value or to sell at the times and prices the subadviser thinks appropriate, and offer greater potential for gain and loss.

GROWTH STYLE RISK. The fund's investments may not have the growth potential originally expected. Growth stocks may fall out of favor with investors and underperform the overall equity market.

PORTFOLIO SELECTION RISK. The subadviser's judgment about a particular security or issuer, or about the economy or a particular sector, region or market segment, or about an investment strategy, may prove to be incorrect.

RISKS OF NON-U.S. INVESTMENTS. Investing in non-U.S. issuers, or in U.S. issuers that have significant exposure to foreign markets, may involve unique risks compared to investing in securities of U.S. issuers. These risks are more pronounced for issuers in emerging markets or to the extent that the fund invests significantly in one region or country. These risks may include different financial reporting practices and regulatory standards, less liquid trading markets, extreme price volatility, currency risks, changes in economic, political, regulatory and social conditions, sustained economic downturns, financial instability, tax burdens, and investment and repatriation restrictions. Lack of information and less market regulation also may affect the value of these securities. Withholding and other non-U.S. taxes may decrease the fund's return. Non-U.S. issuers may be located in parts of the world that have historically been prone to natural disasters. Investing in depositary receipts is subject to many of the same risks as investing directly in non-U.S. issuers. Depositary receipts may involve higher expenses and may trade at a discount (or premium) to the underlying security.

RISKS OF INVESTMENTS IN REITS. Investments in real estate securities are affected by economic conditions, interest rates, governmental actions and other factors. In addition, investing in REITs involves unique risks. They are significantly affected by the market for real estate and are dependent upon management skills and cash flow. REITs may have lower trading volumes and may be subject to more abrupt or erratic price movements than the overall securities markets. Mortgage REITs are particularly subject to interest rate and credit risks. In addition to its own expenses, the fund will indirectly bear its proportionate share of any management and other expenses paid by REITs in which it invests. Many real estate companies, including REITs, utilize leverage.

RISKS OF WARRANTS AND RIGHTS. If the price of the underlying stock does not rise above the exercise price before the warrant expires, the warrant generally expires without any value and the fund loses any amount it paid for the warrant. The failure to exercise subscription rights to purchase common shares would result in the dilution of the fund's interest in the issuing company.

PREFERRED STOCKS RISK. Preferred stocks may pay fixed or adjustable rates of return. Preferred stocks are subject to issuer-specific and market risks applicable generally to equity securities. In addition, a company's preferred stocks generally pay dividends only after the company makes required payments to holders of its bonds and other debt. Thus, the value of preferred stocks will usually react more strongly than bonds and other debt to actual or perceived changes in the company's financial condition or prospects. The market value of preferred stocks generally decreases when interest rates rise. Preferred stocks of smaller companies may be more vulnerable to adverse developments than preferred stocks of larger companies.

RISKS OF CONVERTIBLE SECURITIES. The market values of convertible securities tend to decline as interest rates increase and, conversely, to increase as interest rates decline. A downturn in equity markets may cause the price of convertible securities to decrease relative to other fixed income securities.

DEBT SECURITIES RISK. Factors that could contribute to a decline in the market value of debt securities in the fund include rising interest rates, if the issuer or other obligor of a security held by the fund fails to pay principal and/or interest, otherwise defaults or has its credit rating downgraded or is perceived to be less creditworthy or the credit quality or value of any underlying assets declines. Junk bonds involve greater risk of loss, are subject to greater price volatility and are less liquid, especially during periods of economic uncertainty or change, than higher quality debt securities; they may also be more difficult to value. Junk bonds have a higher risk of default or are already in default and are considered speculative.

MARKET SEGMENT RISK. To the extent the fund emphasizes, from time to time, investments in a market segment, the fund will be subject to a greater degree to the risks particular to that segment, and may experience greater market fluctuation than a fund without the same focus.

DERIVATIVES RISK. Using stock index futures and options and other derivatives can increase fund losses and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves behave in a way not anticipated by the fund. Using derivatives may increase the volatility of the fund's net asset value and may not provide the result intended. Derivatives may have a leveraging effect on the fund. Some derivatives have the potential for unlimited loss, regardless of the size of the fund's initial investment. Changes in a derivative's value may not correlate well with the referenced asset or metric. The fund also may have to sell assets at inopportune times to satisfy its obligations. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. New regulations are changing the derivatives markets. The regulations may make using derivatives more costly, may limit their availability, or may otherwise adversely affect their value or performance. For derivatives that are required to be traded through a clearinghouse or exchange, the fund also will be exposed to the credit risk of the clearinghouse and the broker that submits trades for the fund. It is possible that certain derivatives that are required to be cleared, such as certain swap contracts, will not be accepted for clearing. In addition, regulated trading facilities for swap contracts are relatively new; they may not function as intended, which could impair the ability to enter into swap contracts. The extent and impact of the new regulations are not yet fully known and may not be for some time.

RISKS OF INITIAL PUBLIC OFFERINGS. Companies involved in initial public offerings (IPOs) generally have limited operating histories, and prospects for future profitability are uncertain. Information about the companies may be available for very limited periods. The market for IPO issuers has been volatile, and share prices of newly public companies have fluctuated significantly over short periods of time. Further, stocks of newly-public companies may decline shortly after the IPO. There is no assurance that the fund will have access to IPOs. The purchase of IPO shares may involve high transaction costs.

RISKS OF INVESTMENT IN OTHER FUNDS. Investing in other investment companies, including exchange-traded funds (ETFs), subjects the fund to the risks of investing in the underlying securities or assets held by those funds. When investing in another fund, the fund will bear a pro rata portion of the underlying fund's expenses, in addition to its own expenses.

LEVERAGING RISK. The value of your investment may be more volatile and other risks tend to be compounded if the fund borrows or uses derivatives or other investments, such as ETFs, that have embedded leverage. Leverage generally magnifies the effect of any increase or decrease in the value of the fund's underlying assets or creates investment risk with respect to a larger pool of assets than the fund would otherwise have, potentially resulting in the loss of all assets. Engaging in such transactions may cause the fund to liquidate positions when it may not be advantageous to do so to satisfy its obligations or meet segregation requirements.

EXPENSE RISK. Your actual costs of investing in the fund may be higher than the expenses shown in "Annual fund operating expenses" for a variety of reasons. For example, expense ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile.

Please note that there are many other factors that could adversely affect your investment and that could prevent the fund from achieving its goals.

An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

THE FUND'S PAST PERFORMANCE

The bar chart and table indicate the risks and volatility of an investment in the fund by showing how the fund has performed in the past. The bar chart shows changes in the performance of the fund's Class A shares from calendar year to calendar year. The table shows the average annual total returns for each class of the fund over time and compares these returns to the returns of the Russell 2000 Index and the Russell 2000 Growth Index, each a broad-based measure of market performance that has characteristics relevant to the fund's investment strategies. You can obtain updated performance information by visiting https://us.pioneerinvestments.com/performance or by calling 1-800-225-6292.

The fund acquired the assets and liabilities of Oak Ridge Small Cap Equity Fund (the predecessor fund) on February 13, 2004. As a result of the reorganization, the fund is the accounting successor of the predecessor fund.

In the reorganization, the predecessor fund exchanged its assets for Class A and Class C shares of the fund. The performance of Class A, Class B and Class C shares of the fund is the net asset value performance of the predecessor fund's Class A shares (Class C shares in the case of the fund's Class C shares) prior to the reorganization, restated to reflect differences in any applicable sales charges and Rule 12b-1 fees (but not other differences in expenses). This adjustment had the effect of reducing the previously reported performance of the predecessor fund.

The fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

The bar chart does not reflect any sales charge you may pay when you buy fund shares. If this amount was reflected, returns would be less than those shown.

ANNUAL RETURN CLASS A SHARES (%)

(Year ended December 31)

For the period covered by the bar chart:
THE HIGHEST CALENDAR QUARTERLY RETURN WAS 20.45% (04/01/2009 TO 06/30/2009).

THE LOWEST CALENDAR QUARTERLY RETURN WAS -22.25% (10/01/2008  TO 12/31/2008).

AVERAGE ANNUAL TOTAL RETURN (%)

(for periods ended December 31, 2013)

Average Annual Total Returns Pioneer Oak Ridge Small Cap Growth Fund	1 YEAR	5 YEARS	10 YEARS	SINCE INCEPTION	INCEPTION DATE
Class A	30.98%	18.89%	9.85%	10.83%	Jan. 03, 1994
Class A Return after taxes on distributions	29.47%	18.33%	9.35%	9.96%	Jan. 03, 1994
Class A Return after taxes on distributions and sale of shares	18.72%	15.44%	8.13%	9.12%	Jan. 03, 1994
Class B	33.75%	19.23%		9.33%	Feb. 17, 2004
Class C	37.99%	19.34%	9.61%	8.59%	Mar. 01, 1997
Class K	39.73%			37.83%	Dec. 20, 2012
Class R	38.77%			22.72%	Apr. 02, 2012
Class Y	39.55%			18.91%	Dec. 29, 2009
Russell 2000 Index (reflects no deduction for fees, expenses or taxes)	38.82%	20.08%	9.07%	9.32%	Jan. 03, 1994
Russell 2000 Growth Index (reflects no deduction for fees, expenses or taxes)	43.30%	22.58%	9.41%	7.46%	Jan. 03, 1994

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor's tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.

After-tax returns are shown only for Class A shares. After-tax returns for Class B, Class C, Class K, Class R and Class Y shares will vary.

[1] The fund's investment adviser has contractually agreed to limit ordinary operating expenses (ordinary operating expenses means all fund expenses other than extraordinary expenses, such as litigation, taxes, brokerage commissions and acquired fund fees and expenses) to the extent required to reduce fund expenses to 2.30% and 1.60% of the average daily net assets attributable to Class B and Class R, respectively. These expense limitations are in effect through April 1, 2015. There can be no assurance that the adviser will extend the expense limitation beyond such time. Net expenses for a class may exceed the applicable expense limitation to the extent that the fund incurs excluded expenses. While in effect, an arrangement may be terminated for a class only by agreement of the adviser and the Board of Trustees.