485BPOS 2012-06-30 0000867969 2012-10-28 MFS INSTITUTIONAL TRUST false 2012-10-25 2012-10-28 <tt>The fund pays transaction costs, such as commissions, when it buys and sells<br />securities (or "turns over" its portfolio). A higher portfolio turnover rate <br />may indicate higher transaction costs and may result in higher taxes when <br />shares are held in a taxable account. These transaction costs, which are not <br />reflected in "Annual Fund Operating Expenses" or in the "Example," affect the <br />fund's performance. During the most recent fiscal year, the fund's portfolio <br />turnover rate was 18% of the average value of its portfolio.</tt> <div style="display:none">~ http://www.mfs.com/role/ExpenseExample_S000002540Member column dei_LegalEntityAxis compact * column rr_ProspectusShareClassAxis compact * row primary compact * ~</div> <div style="display:none">~ http://www.mfs.com/role/BarChartData_S000002540Member column dei_LegalEntityAxis compact * column rr_ProspectusShareClassAxis compact * row primary compact * ~</div> <tt>The fund's investment objective is to seek capital appreciation.</tt> <tt>This example is intended to help you compare the cost of investing in the fund<br />with the cost of investing in other mutual funds.<br /><br />The example assumes that: you invest $10,000 in the fund for the time periods<br />indicated and you redeem your shares at the end of the time periods; your<br />investment has a 5% return each year; and the fund's operating expenses remain<br />the same.</tt> Performance Table. Reflects no deduction for fees, expenses or taxes <tt>MFS (Massachusetts Financial Services Company, the fund's investment adviser)<br />normally invests at least 80% of the fund's net assets in issuers with large<br />market capitalizations. MFS generally defines large market capitalization<br />issuers as issuers with market capitalizations of at least $5 billion at the<br />time of purchase.<br /><br />MFS normally invests the fund's assets primarily in U.S. equity securities.<br />Equity securities include common stocks, preferred stocks, securities<br />convertible into stocks, and depositary receipts for those securities.<br /><br />MFS focuses on investing the fund's assets in the stocks of companies it<br />believes are undervalued compared to their perceived worth (value companies).<br /><br />MFS uses a bottom-up investment approach to buying and selling investments for<br />the fund. Investments are selected primarily based on fundamental analysis of<br />individual issuers. Quantitative models that systematically evaluate issuers may<br />also be considered.</tt> Summary of Key Information Example 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. Investment Objective The fund's past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. Principal Risks 2013-10-31 Although your actual costs will likely be higher or lower, under these assumptions your costs would be: 0.18 Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. Bar Chart. Performance Information <tt>After-tax returns are calculated using the historical highest individual federal<br />marginal income tax rates and do not reflect the impact of state and local taxes. <br />Your actual after-tax returns will depend on your own tax situation, and may <br />differ from those shown. The after-tax returns shown are not relevant to investors <br />who hold their shares through tax-deferred arrangements, such as 401(k) plans or <br />individual retirement accounts.</tt> The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. <tt>The total return for the nine-month period ended September 30, 2012, was 15.52%.<br />During the period(s) shown in the bar chart, the highest quarterly return was<br />16.86% (for the calendar quarter ended June 30, 2009) and the lowest quarterly<br />return was (19.05)% (for the calendar quarter ended December 31, 2008).</tt> 1-877-960-6077 Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment): Average Annual Total Returns (for the Periods Ended December 31, 2011) Portfolio Turnover <tt>As with any mutual fund, the fund may not achieve its objective and/or you could lose <br />money on your investment in the fund. An investment in the fund is not a bank deposit <br />and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any <br />other governmental agency.<br /><br />The principal risks of investing in the fund are:<br /><br />Stock Market/Company Risk:&#xA0;&#xA0;Stock markets are volatile and can decline significantly <br />in response to issuer, market, economic, industry, political, regulatory, geopolitical, <br />and other conditions, as well as to investor perceptions of these conditions. The <br />price of an equity security can decrease significantly in response to these conditions, <br />and these conditions can affect a single issuer or type of security, issuers within a <br />broad market sector, industry or geographic region, or the market in general.<br /><br />Value Company Risk:&#xA0;&#xA0;The stocks of value companies can continue to be undervalued for <br />long periods of time and not realize their expected value and can be more volatile than <br />the market in general.<br /><br />Investment Selection Risk:&#xA0;&#xA0;MFS' investment analysis and its selection of investments <br />may not produce the intended results and/or can lead to an investment focus that results <br />in the fund underperforming other funds with similar investment strategies and/or <br />underperforming the markets in which the fund invests.<br /><br />Liquidity Risk:&#xA0;&#xA0;It may not be possible to sell certain investments, types of investments, <br />and/or segments of the market at any particular time or at an acceptable price.</tt> Fees and Expenses Principal Investment Strategies mfs.com <tt>The bar chart and performance table below are intended to provide some indication <br />of the risks of investing in the fund by showing changes in the fund's performance <br />over time and how the fund's performance over time compares with that of a broad <br />measure of market performance.<br /><br />The fund's past performance (before and after taxes) does not necessarily indicate <br />how the fund will perform in the future. Updated performance is available online at <br />mfs.com or by calling 1-877-960-6077.</tt> <tt>This table describes the fees and expenses that you may pay when you buy and<br />hold shares of the fund.</tt> <div style="display:none">~ http://www.mfs.com/role/OperatingExpensesData_S000002540Member column dei_LegalEntityAxis compact * column rr_ProspectusShareClassAxis compact * row primary compact * ~</div> <div style="display:none">~ http://www.mfs.com/role/PerformanceTableData_S000002540Member column dei_LegalEntityAxis compact * column rr_ProspectusShareClassAxis compact * column rr_PerformanceMeasureAxis compact * row primary compact * ~</div> 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 governmental agency. Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell 1000 Value Index 0.0039 -0.0264 0.0389 Fund's Shares Returns After Taxes on Distributions and Sale of Fund Shares 0.0083 -0.0051 0.0374 Fund's Shares Returns After Taxes on Distributions -0.0077 -0.0145 0.0354 ILVAX -0.1427 the lowest quarterly return the highest quarterly return 2012-09-30 Fund Shares Returns Before Taxes 66 2009-06-30 212 -0.1905 0.1598 -0.0002 0.1130 833 371 0.0828 0.1686 -0.0008 0.0012 -0.3234 0.0055 2008-12-31 0.2099 -0.0029 0.0684 The total return for the nine-month period ended -0.0008 0.2563 0.00 0.0479 0.0065 0.0067 0.2138 0.1552 <tt>The fund pays transaction costs, such as commissions, when it buys and sells<br />securities (or "turns over" its portfolio). A higher portfolio turnover rate <br />may indicate higher transaction costs and may result in higher taxes when <br />shares are held in a taxable account. These transaction costs, which are not <br />reflected in "Annual Fund Operating Expenses" or in the "Example," affect the <br />fund's performance. During the most recent fiscal year, the fund's portfolio <br />turnover rate was 22% of the average value of its portfolio.</tt> <div style="display:none">~ http://www.mfs.com/role/ExpenseExample_S000002537Member column dei_LegalEntityAxis compact * column rr_ProspectusShareClassAxis compact * row primary compact * ~</div> <div style="display:none">~ http://www.mfs.com/role/BarChartData_S000002537Member column dei_LegalEntityAxis compact * column rr_ProspectusShareClassAxis compact * row primary compact * ~</div> <tt>The fund's investment objective is to seek capital appreciation.</tt> <tt>This example is intended to help you compare the cost of investing in the fund<br />with the cost of investing in other mutual funds.<br /><br />The example assumes that: you invest $10,000 in the fund for the time periods<br />indicated and you redeem your shares at the end of the time periods; your<br />investment has a 5% return each year; and the fund's operating expenses remain<br />the same.</tt> Performance Table. Reflects no deduction for fees, expenses or taxes <tt>MFS (Massachusetts Financial Services Company, the fund's investment adviser)<br />normally invests at least 80% of the fund's net assets in equity securities.<br /><br />Equity securities include common stocks, preferred stocks, securities convertible <br />into stocks, and depositary receipts for those securities.<br /><br />MFS normally invests the fund's assets primarily in foreign securities, including <br />emerging market securities.<br /><br />MFS may invest a large percentage of the fund's assets in issuers in a single <br />country, a small number of countries, or a particular geographic region.<br /><br />In selecting investments for the fund, MFS is not constrained to any particular<br />investment style. MFS may invest the fund's assets in the stocks of companies it<br />believes to have above average earnings growth potential compared to other companies <br />(growth companies), in the stocks of companies it believes are undervalued compared <br />to their perceived worth (value companies), or in a combination of growth and value <br />companies.<br /><br />MFS may invest the fund's assets in companies of any size.<br /><br />MFS uses a bottom-up investment approach to buying and selling investments for the <br />fund. Investments are selected primarily based on fundamental analysis of individual <br />issuers. Quantitative models that systematically evaluate issuers may also be <br />considered.</tt> Summary of Key Information Example 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. Investment Objective The fund's past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. Principal Risks 2013-10-31 Although your actual costs will likely be higher or lower, under these assumptions your costs would be: 0.22 Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. Bar Chart. Performance Information <tt>After-tax returns are calculated using the historical highest individual federal<br />marginal income tax rates and do not reflect the impact of state and local taxes. <br />Your actual after-tax returns will depend on your own tax situation, and may <br />differ from those shown. The after-tax returns shown are not relevant to <br />investors who hold their shares through tax-deferred arrangements, such as 401(k) <br />plans or individual retirement accounts.</tt> The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. <tt>The total return for the nine-month period ended September 30, 2012, was 12.94%.<br />During the period(s) shown in the bar chart, the highest quarterly return was<br />21.13% (for the calendar quarter ended September 30, 2009) and the lowest<br />quarterly return was (20.30)% (for the calendar quarter ended September 30, 2011).</tt> 1-877-960-6077 Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment): Average Annual Total Returns (for the Periods Ended December 31, 2011) Portfolio Turnover <tt>As with any mutual fund, the fund may not achieve its objective and/or you could<br />lose money on your investment in the fund. An investment in the fund is not a<br />bank deposit and is not insured or guaranteed by the Federal Deposit Insurance<br />Corporation or any other governmental agency.<br /> <br />The principal risks of investing in the fund are:<br /><br />Stock Market/Company Risk:&#xA0;&#xA0;Stock markets are volatile and can decline <br />significantly in response to issuer, market, economic, industry, political, <br />regulatory, geopolitical, and other conditions, as well as to investor <br />perceptions of these conditions. The price of an equity security can decrease <br />significantly in response to these conditions, and these conditions can affect <br />a single issuer or type of security, issuers within a broad market sector, <br />industry or geographic region, or the market in general.<br /><br />Foreign and Emerging Markets Risk:&#xA0;&#xA0;Exposure to foreign markets, especially<br />emerging markets, through issuers or currencies can involve additional risks<br />relating to market, economic, political, regulatory, geopolitical, or other<br />conditions. These factors can make foreign investments, especially those in<br />emerging markets, more volatile and less liquid than U.S. investments. In<br />addition, foreign markets can react differently to these conditions than the<br />U.S. market. Emerging markets can have less developed markets, greater custody<br />and operational risk, and less developed legal, regulatory, and accounting<br />systems, and greater political, social, and economic instability than developed<br />markets.<br /><br />Currency Risk:&#xA0;&#xA0;The value of foreign currencies relative to the U.S. dollar<br />fluctuates in response to market, economic, political, regulatory, geopolitical<br />or other conditions, and a decline in the value of a foreign currency versus the<br />U.S. dollar reduces the value in U.S. dollars of investments denominated in that<br />foreign currency.<br /><br />Geographic Concentration Risk:&#xA0;&#xA0;The fund's performance could be closely tied to<br />the market, currency, economic, political, regulatory, geopolitical, or other<br />conditions in the countries or regions in which the fund invests and could be<br />more volatile than the performance of more geographically-diversified funds.<br /><br />Investment Selection Risk:&#xA0;&#xA0;MFS' investment analysis and its selection of<br />investments may not produce the intended results and/or can lead to an<br />investment focus that results in the fund underperforming other funds with<br />similar investment strategies and/or underperforming the markets in which the<br />fund invests.<br /><br />Liquidity Risk:&#xA0;&#xA0;It may not be possible to sell certain investments, types of<br />investments, and/or segments of the market at any particular time or at an<br />acceptable price.</tt> Fees and Expenses Principal Investment Strategies mfs.com <tt>The bar chart and performance table below are intended to provide some indication <br />of the risks of investing in the fund by showing changes in the fund's performance <br />over time and how the fund's performance over time compares with that of a broad <br />measure of market performance.<br /><br />The fund's past performance (before and after taxes) does not necessarily indicate <br />how the fund will perform in the future. Updated performance is available online at <br />mfs.com or by calling 1-877-960-6077.</tt> <tt>This table describes the fees and expenses that you may pay when you buy and<br />hold shares of the fund.</tt> <div style="display:none">~ http://www.mfs.com/role/OperatingExpensesData_S000002537Member column dei_LegalEntityAxis compact * column rr_ProspectusShareClassAxis compact * row primary compact * ~</div> <div style="display:none">~ http://www.mfs.com/role/PerformanceTableData_S000002537Member column dei_LegalEntityAxis compact * column rr_ProspectusShareClassAxis compact * column rr_PerformanceMeasureAxis compact * row primary compact * ~</div> 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 governmental agency. Index Comparison (Reflects no deduction for fees, expenses or taxes) MSCI EAFE (Europe, Australasia, Far East) Index (gross div) -0.1173 -0.0426 0.0512 Fund's Shares Returns After Taxes on Distributions and Sale of Fund Shares -0.0583 -0.0082 0.0619 Fund's Shares Returns After Taxes on Distributions -0.0975 -0.0148 0.0647 MIEIX -0.0657 the lowest quarterly return the highest quarterly return 2012-09-30 Fund Shares Returns Before Taxes 77 2009-09-30 246 -0.2030 0.1886 -0.0003 0.1097 963 430 0.0911 0.2113 -0.0955 0.0007 -0.3495 0.0071 2011-09-30 0.3312 -0.0106 0.1292 The total return for the nine-month period ended -0.0955 0.3102 0.00 0.0714 0.0075 0.0078 0.2794 0.1294 0000867969 ck0000867969:SummaryS000002537Memberck0000867969:S000002537Memberck0000867969:C000006994Member 2012-10-28 2012-10-28 0000867969 ck0000867969:SummaryS000002537Memberck0000867969:S000002537Memberrr:AfterTaxesOnDistributionsMemberck0000867969:C000006994Member 2012-10-28 2012-10-28 0000867969 ck0000867969:SummaryS000002537Memberck0000867969:S000002537Memberrr:AfterTaxesOnDistributionsAndSalesMemberck0000867969:C000006994Member 2012-10-28 2012-10-28 0000867969 ck0000867969:SummaryS000002537Memberck0000867969:S000002537Memberck0000867969:RRINDEX00001Member 2012-10-28 2012-10-28 0000867969 ck0000867969:SummaryS000002537Memberck0000867969:S000002537Member 2012-10-28 2012-10-28 0000867969 ck0000867969:SummaryS000002540Memberck0000867969:S000002540Memberck0000867969:C000006997Member 2012-10-28 2012-10-28 0000867969 ck0000867969:SummaryS000002540Memberck0000867969:S000002540Memberrr:AfterTaxesOnDistributionsMemberck0000867969:C000006997Member 2012-10-28 2012-10-28 0000867969 ck0000867969:SummaryS000002540Memberck0000867969:S000002540Memberrr:AfterTaxesOnDistributionsAndSalesMemberck0000867969:C000006997Member 2012-10-28 2012-10-28 0000867969 ck0000867969:SummaryS000002540Memberck0000867969:S000002540Memberck0000867969:RRINDEX00002Member 2012-10-28 2012-10-28 0000867969 ck0000867969:SummaryS000002540Memberck0000867969:S000002540Member 2012-10-28 2012-10-28 0000867969 2012-10-28 2012-10-28 pure iso4217:USD Massachusetts Financial Services Company has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity), such that "Total Annual Fund Operating Expenses" do not exceed 0.75% of the fund's average daily net assets annually. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least October 31, 2013. Massachusetts Financial Services Company has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity), such that "Total Annual Fund Operating Expenses" do not exceed 0.65% of the fund's average daily net assets annually. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least October 31, 2013.