485BPOS

                                                            File No. 333-108472
                                                                      811-21425

As filed with the Securities and Exchange Commission on January 4, 2013

                       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. 21              [X]

                                     and/or

             REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY
                               ACT OF 1940                         [X]

                                Amendment No. 23                   [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, Secretary, Pioneer Series Trust I
                  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.

This filing relates solely to Pioneer Oak Ridge Small Cap Growth  Fund,
a series of the Registrant.




                                   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 of 1933 and has duly caused this
Post-Effective Amendment No. 21 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 4th day of January, 2013.

                                      PIONEER SERIES TRUST I

                                  By: /s/ Daniel K. Kingsbury
                                      ----------------------------
                                      Daniel K. Kingsbury
                                      Executive Vice 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 January 4, 2013:

        Signature                               Title

        /s/ John F. Cogan, Jr.*                 President (Principal Executive
        ---------------------------             Officer) and Trustee
        John F. Cogan, Jr.

        /s/ Mark E. Bradley*                    Treasurer (Principal Financial
        ---------------------------             and Accounting Officer)
        Mark E. Bradley

        /s/ David R. Bock*                      Trustee
        ---------------------------
        David R. Bock

        /s/ Benjamin M. Friedman*               Trustee
        ---------------------------
        Benjamin M. Friedman

        /s/ Margaret B. W. Graham*              Trustee
        ---------------------------
        Margaret B. W. Graham

        /s/ Daniel K. Kingsbury                 Executive Vice President and
        ---------------------------             Trustee
        Daniel K. Kingsbury

        /s/ Thomas J. Perna*                    Chairman of the Board and
        ---------------------------             Trustee
        Thomas J. Perna

        /s/ Marguerite A. Piret*                Trustee
        ---------------------------
        Marguerite A. Piret

    By: /s/ Daniel K. Kingsbury                 Dated: January 4, 2013
        ---------------------------
        Daniel K. Kingsbury
        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	Dec. 15, 2012
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 30 and the "Sales charges" section of the statement of additional information beginning on page 52.
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, 2014
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 26% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	26.00%
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
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	Other expenses for Class K are based on estimated amounts for the current fiscal year.
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 ($3.70 billion as of December 31, 2011) or the 3-year rolling average of the market capitalization of the largest company within the Russell 2000 Index ($4.01 billion as of December 31, 2011) 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 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. The fund may, but is not required to, use derivatives. The fund may use derivatives for a variety of purposes, including as a hedge against adverse changes in the market prices of securities, interest rates or currency exchange rates; as a substitute for purchasing or selling securities; and to increase the fund’s return as a non-hedging strategy that may be considered speculative. 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 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). The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities of issuers worldwide. Some governmental and non-governmental issuers (notably in Europe) 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. The 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 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 by the countries experiencing these difficulties. In addition, legislation recently enacted in the U.S. is changing many aspects of financial regulation. The impact of the legislation 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. 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 issuers with 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. 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 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. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation is not yet fully known and may not be for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance. 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 includes 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, which has been 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 One Year or Less [Text]	rr_PerformanceOneYearOrLess	No performance information is presented for Class K or Class R shares in the table because Class K and Class R shares do not have annual returns for at least one calendar year.
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.
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). At September 30, 2012, the year-to-date return was 9.29%.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURN (%)  (for periods ended December 31, 2011)
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	The performance of Class A, Class B and Class C shares of the fund includes 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, which has been 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.
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	No performance information is presented for Class K or Class R shares in the table because Class K and Class R shares do not have annual returns for at least one calendar year. The returns for Class K and Class R shares would differ from those of Class A, B, C and Y shares because they have different expenses.
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	0.84%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.42%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.51%	[2]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.11%)	[2]
Net Expenses	rr_NetExpensesOverAssets	1.40%	[2]
1	rr_ExpenseExampleYear01	709
3	rr_ExpenseExampleYear03	1,015
5	rr_ExpenseExampleYear05	1,342
10	rr_ExpenseExampleYear10	2,264
1	rr_ExpenseExampleNoRedemptionYear01	709
3	rr_ExpenseExampleNoRedemptionYear03	1,015
5	rr_ExpenseExampleNoRedemptionYear05	1,342
10	rr_ExpenseExampleNoRedemptionYear10	2,264
2002	rr_AnnualReturn2002	(19.35%)
2003	rr_AnnualReturn2003	36.90%
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%
Year to Date Return, Label	rr_YearToDateReturnLabel	the year-to-date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	9.29%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	THE 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	THE LOWEST CALENDAR QUARTERLY RETURN
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(22.25%)
1 YEAR	rr_AverageAnnualReturnYear01	(4.89%)
5 YEARS	rr_AverageAnnualReturnYear05	3.68%
10 YEARS	rr_AverageAnnualReturnYear10	6.28%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	9.45%
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	0.84%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.55%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.39%	[2]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.09%)	[2]
Net Expenses	rr_NetExpensesOverAssets	2.30%	[2]
1	rr_ExpenseExampleYear01	633
3	rr_ExpenseExampleYear03	1,037
5	rr_ExpenseExampleYear05	1,367
10	rr_ExpenseExampleYear10	2,501
1	rr_ExpenseExampleNoRedemptionYear01	233
3	rr_ExpenseExampleNoRedemptionYear03	737
5	rr_ExpenseExampleNoRedemptionYear05	1,267
10	rr_ExpenseExampleNoRedemptionYear10	2,501
1 YEAR	rr_AverageAnnualReturnYear01	(3.81%)
5 YEARS	rr_AverageAnnualReturnYear05	3.97%
10 YEARS	rr_AverageAnnualReturnYear10
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	6.13%
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	0.84%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.33%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.17%	[2]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Net Expenses	rr_NetExpensesOverAssets	2.17%	[2]
1	rr_ExpenseExampleYear01	320
3	rr_ExpenseExampleYear03	679
5	rr_ExpenseExampleYear05	1,164
10	rr_ExpenseExampleYear10	2,503
1	rr_ExpenseExampleNoRedemptionYear01	220
3	rr_ExpenseExampleNoRedemptionYear03	679
5	rr_ExpenseExampleNoRedemptionYear05	1,164
10	rr_ExpenseExampleNoRedemptionYear10	2,503
1 YEAR	rr_AverageAnnualReturnYear01	0.14%
5 YEARS	rr_AverageAnnualReturnYear05	4.02%
10 YEARS	rr_AverageAnnualReturnYear10	6.04%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	6.78%
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	0.84%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.08%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.92%	[2]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Net Expenses	rr_NetExpensesOverAssets	0.92%	[2]
1	rr_ExpenseExampleYear01	94
3	rr_ExpenseExampleYear03	293
5	rr_ExpenseExampleYear05	509
10	rr_ExpenseExampleYear10	1,131
1	rr_ExpenseExampleNoRedemptionYear01	94
3	rr_ExpenseExampleNoRedemptionYear03	293
5	rr_ExpenseExampleNoRedemptionYear05	509
10	rr_ExpenseExampleNoRedemptionYear10	1,131
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	0.84%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other Expenses	rr_OtherExpensesOverAssets	0.60%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.94%	[2]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.34%)	[2]
Net Expenses	rr_NetExpensesOverAssets	1.60%	[2]
1	rr_ExpenseExampleYear01	163
3	rr_ExpenseExampleYear03	576
5	rr_ExpenseExampleYear05	1,016
10	rr_ExpenseExampleYear10	2,237
1	rr_ExpenseExampleNoRedemptionYear01	163
3	rr_ExpenseExampleNoRedemptionYear03	576
5	rr_ExpenseExampleNoRedemptionYear05	1,016
10	rr_ExpenseExampleNoRedemptionYear10	2,237
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	0.84%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.19%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.03%	[2]
Less: Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Net Expenses	rr_NetExpensesOverAssets	1.03%	[2]
1	rr_ExpenseExampleYear01	105
3	rr_ExpenseExampleYear03	328
5	rr_ExpenseExampleYear05	569
10	rr_ExpenseExampleYear10	1,259
1	rr_ExpenseExampleNoRedemptionYear01	105
3	rr_ExpenseExampleNoRedemptionYear03	328
5	rr_ExpenseExampleNoRedemptionYear05	569
10	rr_ExpenseExampleNoRedemptionYear10	1,259
1 YEAR	rr_AverageAnnualReturnYear01	1.22%
5 YEARS	rr_AverageAnnualReturnYear05
10 YEARS	rr_AverageAnnualReturnYear10
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	13.62%
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	(5.62%)
5 YEARS	rr_AverageAnnualReturnYear05	3.17%
10 YEARS	rr_AverageAnnualReturnYear10	5.96%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	8.60%
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	(2.26%)
5 YEARS	rr_AverageAnnualReturnYear05	3.08%
10 YEARS	rr_AverageAnnualReturnYear10	5.48%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	8.16%
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	(4.18%)
5 YEARS	rr_AverageAnnualReturnYear05	0.15%
10 YEARS	rr_AverageAnnualReturnYear10	5.62%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	7.50%
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	(2.91%)
5 YEARS	rr_AverageAnnualReturnYear05	2.09%
10 YEARS	rr_AverageAnnualReturnYear10	4.48%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	5.38%
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Jan. 03, 1994

[1] Other expenses for Class K are based on estimated amounts for the current fiscal year.

[2] 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 and brokerage commissions) to the extent required to reduce fund expenses to 1.40%, 2.30%, and 1.60% of the average daily net assets attributable to Class A, Class B and Class R shares, respectively. These expense limitations are in effect through April 1, 2014. There can be no assurance that the adviser will extend the expense limitations beyond such times. While in effect, an arrangement may be terminated for a class only by agreement of the adviser and the Board of Trustees.

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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 30 and the "Sales charges" section of the statement of additional information beginning on page 52.

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		0.84%	0.84%	0.84%	0.84%	0.84%	0.84%
Distribution and Service (12b-1) Fees		0.25%	1.00%	1.00%	none	0.50%	none
Other Expenses	[1]	0.42%	0.55%	0.33%	0.08%	0.60%	0.19%
Total Annual Fund Operating Expenses	[2]	1.51%	2.39%	2.17%	0.92%	1.94%	1.03%
Less: Fee Waiver and Expense Reimbursement	[2]	(0.11%)	(0.09%)	none	none	(0.34%)	none
Net Expenses	[2]	1.40%	2.30%	2.17%	0.92%	1.60%	1.03%

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	1,015	1,342	2,264
Class B	633	1,037	1,367	2,501
Class C	320	679	1,164	2,503
Class K	94	293	509	1,131
Class R	163	576	1,016	2,237
Class Y	105	328	569	1,259

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	1,015	1,342	2,264
Class B	233	737	1,267	2,501
Class C	220	679	1,164	2,503
Class K	94	293	509	1,131
Class R	163	576	1,016	2,237
Class Y	105	328	569	1,259

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 26% 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 ($3.70 billion as of December 31, 2011) or the 3-year rolling average of the market capitalization of the largest company within the Russell 2000 Index ($4.01 billion as of December 31, 2011) 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 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.

The fund may, but is not required to, use derivatives. The fund may use derivatives for a variety of purposes, including as a hedge against adverse changes in the market prices of securities, interest rates or currency exchange rates; as a substitute for purchasing or selling securities; and to increase the fund’s return as a non-hedging strategy that may be considered speculative. 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 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). The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities of issuers worldwide. Some governmental and non-governmental issuers (notably in Europe) 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. The 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 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 by the countries experiencing these difficulties. In addition, legislation recently enacted in the U.S. is changing many aspects of financial regulation. The impact of the legislation 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.

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 issuers with 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.

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 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. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation is not yet fully known and may not be for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance.

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 includes 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, which has been 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).

At September 30, 2012, the year-to-date return was 9.29%.

No performance information is presented for Class K or Class R shares in the table because Class K and Class R shares do not have annual returns for at least one calendar year. The returns for Class K and Class R shares would differ from those of Class A, B, C and Y shares because they have different expenses.

AVERAGE ANNUAL TOTAL RETURN (%)
 (for periods ended December 31, 2011)

Average Annual Total Returns Pioneer Oak Ridge Small Cap Growth Fund	1 YEAR	5 YEARS	10 YEARS	SINCE INCEPTION	INCEPTION DATE
Class A	(4.89%)	3.68%	6.28%	9.45%	Jan. 03, 1994
Class A Return after taxes on distributions	(5.62%)	3.17%	5.96%	8.60%	Jan. 03, 1994
Class A Return after taxes on distributions and sale of shares	(2.26%)	3.08%	5.48%	8.16%	Jan. 03, 1994
Class B	(3.81%)	3.97%		6.13%	Feb. 17, 2004
Class C	0.14%	4.02%	6.04%	6.78%	Mar. 01, 1997
Class Y	1.22%			13.62%	Dec. 29, 2009
Russell 2000 Index (reflects no deduction for fees, expenses or taxes)	(4.18%)	0.15%	5.62%	7.50%	Jan. 03, 1994
Russell 2000 Growth Index (reflects no deduction for fees, expenses or taxes)	(2.91%)	2.09%	4.48%	5.38%	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] Other expenses for Class K are based on estimated amounts for the current fiscal year.

[2] 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 and brokerage commissions) to the extent required to reduce fund expenses to 1.40%, 2.30%, and 1.60% of the average daily net assets attributable to Class A, Class B and Class R shares, respectively. These expense limitations are in effect through April 1, 2014. There can be no assurance that the adviser will extend the expense limitations beyond such times. While in effect, an arrangement may be terminated for a class only by agreement of the adviser and the Board of Trustees.

XML

Document and Entity Information	12 Months Ended
	Dec. 15, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	Dec. 14, 2012
Registrant Name	PIONEER SERIES TRUST I
Central Index Key	0001257951
Amendment Flag	false
Document Creation Date	Dec. 14, 2012
Document Effective Date	Dec. 15, 2012
Prospectus Date	Dec. 15, 2012

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	PIONEER SERIES TRUST I
Prospectus Date	rr_ProspectusDate	Dec. 15, 2012
Document Creation Date	dei_DocumentCreationDate	Dec. 14, 2012