0001257951 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member psti1:C000027825Member 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member psti1:C000027826Member 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member psti1:C000027827Member 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member psti1:C000123838Member 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member psti1:C000115369Member 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member psti1:C000082461Member 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member rr:AfterTaxesOnDistributionsMember psti1:C000027825Member 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member rr:AfterTaxesOnDistributionsAndSalesMember psti1:C000027825Member 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member psti1:RussellTwentyHundredIndexMember 2011-12-16 2012-12-15 0001257951 psti1:S000010047Member psti1:RussellTwentyHundredGrowthIndexMember 2011-12-16 2012-12-15 pure iso4217:USD 2012-12-15 485BPOS PIONEER SERIES TRUST I 0001257951 2012-12-14 2012-12-15 false 2012-12-14 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.<br/><br/>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 <br/>&nbsp;&nbsp;(fees paid directly from your investment) ANNUAL FUND OPERATING EXPENSES<br/>&nbsp;(expenses that you pay each year as a percentage of the value of your investment) PORTFOLIO TURNOVER The fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; 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&#8217;s performance. During the most recent fiscal year, the fund&#8217;s portfolio turnover rate was 26% of the average value of its portfolio. 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&#8217;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<br/>NUMBER OF YEARS YOU OWN YOUR SHARES IF YOU DO NOT REDEEM YOUR SHARES<br/> NUMBER OF YEARS YOU OWN YOUR SHARES 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&#8217;s investments will not be confined to securities issued by companies included in the Index. For purposes of the fund&#8217;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.<br/><br/> 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.<br/><br/> 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.<br/><br/> 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&#8217;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.<br/><br/> The fund uses a "growth" style of management and seeks to invest in issuers with above average potential for earnings growth.<br/><br/> When making purchase decisions for the fund, the subadviser uses a disciplined approach that involves three primary components: <ul type="square"><li style="margin-left:-20px"> 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.</li></ul> <ul type="square"><li style="margin-left:-20px"> 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.</li></ul> <ul type="square"><li style="margin-left:-20px"> Valuation - Finally, the subadviser values companies by considering price-to sales ratios and price-to-earnings ratios within a peer group.</li></ul> From this process, the subadviser constructs a list of securities for the fund to purchase.<br/><br/> The subadviser makes sell decisions for the fund based on a number of factors, including deterioration in a company&#8217;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.<br/><br/> 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&#8217;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. <br/><br/> 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.<br/><br/>GROWTH STYLE RISK. The fund&#8217;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.<br/><br/>PORTFOLIO SELECTION RISK. The subadviser&#8217;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.<br/><br/> 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&#8217;s return. Non-U.S. issuers may be located in parts of the world that have historically been prone to natural disasters.<br/><br/> 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.<br/><br/> 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.<br/><br/> 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&#8217;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&#8217;s initial investment. Changes in a derivative&#8217;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.<br/><br/> 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&#8217;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.<br/><br/> 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.<br/><br/> Please note that there are many other factors that could adversely affect your investment and that could prevent the fund from achieving its goals.<br/><br/> 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&#8217;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&#8217;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&#8217;s investment strategies. You can obtain updated performance information by visiting https://us.pioneerinvestments.com/performance or by calling 1-800-225-6292.<br/><br/> 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.<br/><br/> 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&#8217;s Class A shares (Class C shares in the case of the fund&#8217;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.<br/><br/> The fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.<br/><br/>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 (%)<br/>&nbsp;(Year ended December 31) For the period covered by the bar chart:<br/>THE HIGHEST CALENDAR QUARTERLY RETURN WAS 20.45% (04/01/2009 TO 06/30/2009).<br/>THE LOWEST CALENDAR QUARTERLY RETURN WAS -22.25% (10/01/2008 TO 12/31/2008).<br/><br/>At September 30, 2012, the year-to-date return was 9.29%. AVERAGE ANNUAL TOTAL RETURN (%)<br/>&nbsp;(for periods ended December 31, 2011) April 1, 2014 0.26 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. 50000 You could lose money on your investment in the fund. 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 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&#8217;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&#8217;s investment strategies. 1-800-225-6292 https://us.pioneerinvestments.com/performance The fund&#8217;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. 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&#8217;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. Other expenses for Class K are based on estimated amounts for the current fiscal year. 0.0575 0 0 0 0 0 0 0.04 0.01 0 0 0 0.0084 0.0084 0.0084 0.0084 0.0084 0.0084 0.0025 0.01 0.01 0 0.005 0 0.0042 0.0055 0.0033 0.0008 0.006 0.0019 0.0151 0.0239 0.0217 0.0092 0.0194 0.0103 -0.0011 -0.0009 0 0 -0.0034 0 0.014 0.023 0.0217 0.0092 0.016 0.0103 709 633 320 94 163 105 1015 1037 679 293 576 328 1342 1367 1164 509 1016 569 2264 2501 2503 1131 2237 1259 709 233 220 94 163 105 1015 737 679 293 576 328 1342 1267 1164 509 1016 569 2264 2501 2503 1131 2237 1259 -0.1935 0.369 0.226 0.0627 0.067 0.1038 -0.2979 0.2608 0.2891 0.0092 -0.0489 -0.0562 -0.0226 -0.0381 0.0014 0.0122 -0.0418 -0.0291 0.0368 0.0317 0.0308 0.0397 0.0402 0.0015 0.0209 0.0628 0.0596 0.0548 0.0604 0.0562 0.0448 0.0945 0.086 0.0816 0.0613 0.0678 0.1362 0.075 0.0538 1994-01-03 1994-01-03 1994-01-03 2004-02-17 1997-03-01 2009-12-29 1994-01-03 1994-01-03 <div style="display:none">~ http://www.pioneerinvestments.com/role/ScheduleAnnualTotalReturnsPioneerOakRidgeSmallCapGrowthFundBarChart column period compact * ~</div> <div style="display:none">~ http://www.pioneerinvestments.com/role/ScheduleAverageAnnualTotalReturnsTransposedPioneerOakRidgeSmallCapGrowthFund column period compact * ~</div> <div style="display:none">~ http://www.pioneerinvestments.com/role/ScheduleShareholderFeesPioneerOakRidgeSmallCapGrowthFund column period compact * ~</div> <div style="display:none">~ http://www.pioneerinvestments.com/role/ScheduleAnnualFundOperatingExpensesPioneerOakRidgeSmallCapGrowthFund column period compact * ~</div> <div style="display:none">~ http://www.pioneerinvestments.com/role/ScheduleExpenseExampleTransposedPioneerOakRidgeSmallCapGrowthFund column period compact * ~</div> <div style="display:none">~ http://www.pioneerinvestments.com/role/ScheduleExpenseExampleNoRedemptionTransposedPioneerOakRidgeSmallCapGrowthFund column period compact * ~</div> the year-to-date return THE HIGHEST CALENDAR QUARTERLY RETURN THE LOWEST CALENDAR QUARTERLY RETURN 2012-09-30 2009-06-30 2008-12-31 0.0929 0.2045 -0.2225 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). 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. 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&#8217;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.<br/><br/>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. 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. Other expenses for Class K are based on estimated amounts for the current fiscal year. 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.