UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED
MANAGEMENT INVESTMENT COMPANIES

Investment Company Act File Number: 811-05986

T. Rowe Price Index Trust, Inc.

(Exact name of registrant as specified in charter)

100 East Pratt Street, Baltimore, MD 21202

(Address of principal executive offices)

David Oestreicher

100 East Pratt Street, Baltimore, MD 21202

(Name and address of agent for service)

Registrant’s telephone number, including area code: (410) 345-2000

Date of fiscal year end: December 31

Date of reporting period: December 31, 2017

The views and opinions in this report were current as of December 31, 2017. They are not guarantees of performance or investment results and should not be taken as investment advice. Investment decisions reflect a variety of factors, and the managers reserve the right to change their views about individual stocks, sectors, and the markets at any time. As a result, the views expressed should not be relied upon as a forecast of the fund’s future investment intent. The report is certified under the Sarbanes-Oxley Act, which requires mutual funds and other public companies to affirm that, to the best of their knowledge, the information in their financial reports is fairly and accurately stated in all material respects.

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The Mid-Cap Index Fund began operations in 2015 as a T. Rowe Price passively managed fund. The fund is not open for direct purchase by outside investors. It is intended to be used by T. Rowe Price’s asset allocation strategies as an additional investment option, as our actively managed mid-cap strategies are facing capacity constraints.

Mid-cap stocks produced positive results in the period. The Mid-Cap Index Fund returned 20.88% for the period ended December 31, 2017, versus 21.16% for the Russell Select Midcap Index. Fund performance tends to slightly lag that of the benchmark because of the fund’s operating and management expenses. (Performance for the I Class will vary due to its differing fee structure.)

U.S. equities continued to surge higher in 2017, with many benchmarks, including the S&P 500, reaching record or near-record highs. Strong corporate earnings growth, rising business sentiment, and generally positive economic data helped push the profits for S&P 500-listed companies higher. The market generally shrugged off lackluster first-quarter economic growth, three interest rate increases from the U.S. Federal Reserve, President Donald Trump’s domestic political controversies, and Republicans’ failed attempts to repeal the Affordable Care Act. Growth stocks widely outpaced value across the capitalization spectrum. Mid-cap stocks lagged large-caps, but they outperformed small-caps.

In the mid-cap universe, as measured by the Russell Select Midcap Index benchmark, most sectors produced positive returns. Information technology shares fared best, driven by outsized gains in a handful of technology and Internet stocks. Health care, industrials and business services, materials, and financials outperformed the benchmark returns. Only two sectors, telecommunication services and energy, finished 2017 with negative returns. Telecommunication services stocks fell as wireless companies contended with slowing growth. Low oil prices in the first half of the year weighed on the sector. However, cooperation among the world’s major oil producers to curb output helped energy stocks reverse most of their declines by year-end.

The fund seeks to match the investment returns of mid-capitalization U.S. stocks by seeking to replicate the performance of the Russell Select Midcap Index, which also serves as the fund’s primary benchmark. The index, which was created for T. Rowe Price and will be administered by Russell Investment Group, consists of approximately 500 stocks and includes all stocks in the Russell 1000 Index, except for those also included in the S&P 500 Index. The fund seeks to employ a full replication strategy, which involves investing substantially all of its assets in all of the stocks in the index and seeking to maintain holdings of each stock in proportion to its weight in the index.

In line with the allocations in the index, financials and information technology together account for approximately one-third of the fund’s investments. Consumer discretionary, industrials and business services, and real estate are also notable components at the sector level. Utilities and telecommunication services each compose less than 5% of net assets.

Electric car maker Tesla was the largest component in the portfolio, and the stock performed well in the period. Software services company ServiceNow and gaming resorts operator Las Vegas Sands were also among the largest positions at the end of the year, and their contributions were strong. Airline operator JetBlue Airways’ contribution was flat, and retailer JC Penney underperformed the average contribution of all mid-caps in the index. (Please refer to the fund’s portfolio of investments for a complete list of holdings and the amount each represents in the portfolio.)

Top stocks came from a variety of industries, including social network Twitter and restaurant company Yum China. Many of the strongest stocks were from the information technology sector, which was in favor for many investors as growth stocks became more attractive. Data center Ethernet switch maker Arista Networks, semiconductor manufacturer First Solar, and Cognex, which produces software and sensors for automated manufacturing, all saw shares advance. Poor performers were also from a variety of industries, including telecommunications company Sprint.

The outlook for the U.S. stock market is guardedly optimistic. Corporate earnings growth is expected to continue into 2018, and business sentiment is likely to remain positive. A gradual rise in interest rates is not expected to impede the performance of stocks. The trend of synchronized economic growth that began in earnest during the second half of the year is likely to continue into 2018. However, this past year’s rally has left stock valuations looking stretched. Other risks include an increase in inflationary pressure as a result of strong U.S. economic growth, an unanticipated fast rise in interest rates, volatility in energy prices, and negative repercussions from geopolitical tensions.

The committee chairman has day-to-day responsibility for managing the portfolio and works with committee members in developing and executing the fund’s investment program.

As with all stock mutual funds, the fund’s share price can fall because of weakness in the stock market, a particular industry, or specific holdings. Stock markets can decline for many reasons, including adverse political or economic developments, changes in investor psychology, or heavy institutional selling. The prospects for an industry or company may deteriorate because of a variety of factors, including disappointing earnings or changes in the competitive environment.

Russell 1000 Index: An index that tracks the performance of the 1,000 largest companies in the Russell 3000 Index.

Russell Select Midcap Index: An unmanaged index that is designed to measure the performance of the mid-cap segment of the U.S. equity universe. It includes approximately 500 mid-cap U.S. securities based on market capitalization without consideration to a growth or value style.

S&P 500 Index: An unmanaged index that tracks the stocks of 500 primarily large-cap U.S. companies.

Note: Russell Investment Group is the source and owner of the trademarks, service marks, and copyrights related to the Russell indexes. Russell^®is a trademark of Russell Investment Group.

This chart shows the value of a hypothetical $10,000 investment in the fund over the past 10 fiscal year periods or since inception (for funds lacking 10-year records). The result is compared with benchmarks, which may include a broad-based market index and a peer group average or index. Market indexes do not include expenses, which are deducted from fund returns as well as mutual fund averages and indexes.

As a mutual fund shareholder, you may incur two types of costs: (1) transaction costs, such as redemption fees or sales loads, and (2) ongoing costs, including management fees, distribution and service (12b-1) fees, and other fund expenses. The following example is intended to help you understand your ongoing costs (in dollars) of investing in the fund and to compare these costs with the ongoing costs of investing in other mutual funds. The example is based on an investment of $1,000 invested at the beginning of the most recent six-month period and held for the entire period.

Please note that the fund has two share classes: The Investor Class charges no distribution and service (12b-1) fee, and the I Class shares are also available to institutionally oriented clients and impose no 12b-1 or administrative fee payment. Each share class is presented separately in the table.

Actual Expenses
The first line of the following table (Actual) provides information about actual account values and actual expenses. You may use the information on this line, together with your account balance, to estimate the expenses that you paid over the period. Simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number on the first line under the heading “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

Hypothetical Example for Comparison Purposes
The information on the second line of the table (Hypothetical) is based on hypothetical account values and expenses derived from the fund’s actual expense ratio and an assumed 5% per year rate of return before expenses (not the fund’s actual return). You may compare the ongoing costs of investing in the fund with other funds by contrasting this 5% hypothetical example and the 5% hypothetical examples that appear in the shareholder reports of the other funds. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period.

Note: T. Rowe Price charges an account service fee that is not included in the accompanying table. The account service fee is charged on a quarterly basis, usually during the last week of a calendar quarter, and applies to accounts with balances below $10,000 on the day of the assessment. The fee is charged to accounts that fall below $10,000 for any reason, including market fluctuations, redemptions, or exchanges. When an account with less than $10,000 is closed either through redemption or exchange, the fee is charged and deducted from the proceeds. The fee applies to IRAs but not to retirement plans directly registered with T. Rowe Price Services or accounts maintained by intermediaries through NSCC^®Networking. If you are subject to the fee, keep it in mind when you are estimating the ongoing expenses of investing in the fund and when comparing the expenses of this fund with other funds.

You should also be aware that the expenses shown in the table highlight only your ongoing costs and do not reflect any transaction costs, such as redemption fees or sales loads. Therefore, the second line of the table is useful in comparing ongoing costs only and will not help you determine the relative total costs of owning different funds. To the extent a fund charges transaction costs, however, the total cost of owning that fund is higher.

T. Rowe Price Index Trust, Inc. (the corporation) is registered under the Investment Company Act of 1940 (the 1940 Act). The Mid-Cap Index Fund (the fund) is a diversified, open-end management investment company established by the corporation. The fund is available for investment only by mutual funds, college savings plans, and other institutional client accounts managed by T. Rowe Price Associates, Inc., or its affiliates and is not available for direct purchase by members of the public. The fund seeks to track the performance of a benchmark index that measures the investment return of mid-capitalization U.S. stocks. The fund has two classes of shares: the Mid-Cap Index Fund (Investor Class) and the Mid-Cap Index Fund–I Class (I Class). I Class shares generally are available only to investors meeting a $1,000,000 minimum investment or certain other criteria. Each class has exclusive voting rights on matters related solely to that class; separate voting rights on matters that relate to both classes; and, in all other respects, the same rights and obligations as the other class.

Basis of Preparation The fund is an investment company and follows accounting and reporting guidance in the Financial Accounting Standards Board (FASB) Accounting Standards Codification Topic 946 (ASC 946). The accompanying financial statements were prepared in accordance with accounting principles generally accepted in the United States of America (GAAP), including, but not limited to, ASC 946. GAAP requires the use of estimates made by management. Management believes that estimates and valuations are appropriate; however, actual results may differ from those estimates, and the valuations reflected in the accompanying financial statements may differ from the value ultimately realized upon sale or maturity.

Investment Transactions, Investment Income, and Distributions Investment transactions are accounted for on the trade date basis. Income and expenses are recorded on the accrual basis. Realized gains and losses are reported on the identified cost basis. Dividends received from mutual fund investments are reflected as dividend income; capital gain distributions are reflected as realized gain/loss. Dividend income and capital gain distributions are recorded on the ex-dividend date. Income tax-related interest and penalties, if incurred, are recorded as income tax expense. Distributions from REITs are initially recorded as dividend income and, to the extent such represent a return of capital or capital gain for tax purposes, are reclassified when such information becomes available. Income distributions are declared and paid by each class annually. Distributions to shareholders are recorded on the ex-dividend date. A capital gain distribution may also be declared and paid by the fund annually.

Class Accounting Shareholder servicing, prospectus, and shareholder report expenses incurred by each class are charged directly to the class to which they relate. Expenses common to both classes, investment income, and realized and unrealized gains and losses are allocated to the classes based upon the relative daily net assets of each class. To the extent any expenses are waived or reimbursed in accordance with an expense limitation (see Note 5), the waiver or reimbursement is charged to the applicable class or allocated across the classes in the same manner as the related expense.

New Accounting Guidance In March 2017, the FASB issued amended guidance to shorten the amortization period for certain callable debt securities, held at a premium. The guidance is effective for fiscal years and interim periods beginning after December 15, 2018. Adoption will have no effect on the fund’s net assets or results of operations.

On August 1, 2017, the fund implemented amendments to Regulation S-X, issued by the Securities and Exchange Commission, which require standardized, enhanced disclosures, particularly related to derivatives, in investment company financial statements. Adoption had no effect on the fund’s net assets or results of operations.

Indemnification In the normal course of business, the fund may provide indemnification in connection with its officers and directors, service providers, and/or private company investments. The fund’s maximum exposure under these arrangements is unknown; however, the risk of material loss is currently considered to be remote.

The fund’s financial instruments are valued and each class’s net asset value (NAV) per share is computed at the close of the New York Stock Exchange (NYSE), normally 4 p.m. ET, each day the NYSE is open for business. However, the NAV per share may be calculated at a time other than the normal close of the NYSE if trading on the NYSE is restricted, if the NYSE closes earlier, or as may be permitted by the SEC.

Fair Value The fund’s financial instruments are reported at fair value, which GAAP defines as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The T. Rowe Price Valuation Committee (the Valuation Committee) is an internal committee that has been delegated certain responsibilities by the fund’s Board of Directors (the Board) to ensure that financial instruments are appropriately priced at fair value in accordance with GAAP and the 1940 Act. Subject to oversight by the Board, the Valuation Committee develops and oversees pricing-related policies and procedures and approves all fair value determinations. Specifically, the Valuation Committee establishes procedures to value securities; determines pricing techniques, sources, and persons eligible to effect fair value pricing actions; oversees the selection, services, and performance of pricing vendors; oversees valuation-related business continuity practices; and provides guidance on internal controls and valuation-related matters. The Valuation Committee reports to the Board and has representation from legal, portfolio management and trading, operations, risk management, and the fund’s treasurer.

Various valuation techniques and inputs are used to determine the fair value of financial instruments. GAAP establishes the following fair value hierarchy that categorizes the inputs used to measure fair value:

Level 1 – quoted prices (unadjusted) in active markets for identical financial instruments that the fund can access at the reporting date

Level 2 – inputs other than Level 1 quoted prices that are observable, either directly or indirectly (including, but not limited to, quoted prices for similar financial instruments in active markets, quoted prices for identical or similar financial instruments in inactive markets, interest rates and yield curves, implied volatilities, and credit spreads)

Observable inputs are developed using market data, such as publicly available information about actual events or transactions, and reflect the assumptions that market participants would use to price the financial instrument. Unobservable inputs are those for which market data are not available and are developed using the best information available about the assumptions that market participants would use to price the financial instrument. GAAP requires valuation techniques to maximize the use of relevant observable inputs and minimize the use of unobservable inputs. When multiple inputs are used to derive fair value, the financial instrument is assigned to the level within the fair value hierarchy based on the lowest-level input that is significant to the fair value of the financial instrument. Input levels are not necessarily an indication of the risk or liquidity associated with financial instruments at that level but rather the degree of judgment used in determining those values.

Valuation Techniques Equity securities listed or regularly traded on a securities exchange or in the over-the-counter (OTC) market are valued at the last quoted sale price or, for certain markets, the official closing price at the time the valuations are made. OTC Bulletin Board securities are valued at the mean of the closing bid and asked prices. A security that is listed or traded on more than one exchange is valued at the quotation on the exchange determined to be the primary market for such security. Listed securities not traded on a particular day are valued at the mean of the closing bid and asked prices. Actively traded equity securities listed on a domestic exchange generally are categorized in Level 1 of the fair value hierarchy. OTC Bulletin Board securities, certain preferred securities, and equity securities traded in inactive markets generally are categorized in Level 2 of the fair value hierarchy.

Investments in mutual funds are valued at the mutual fund’s closing NAV per share on the day of valuation and are categorized in Level 1 of the fair value hierarchy. Assets and liabilities other than financial instruments, including short-term receivables and payables, are carried at cost, or estimated realizable value, if less, which approximates fair value.

Thinly traded financial instruments and those for which the above valuation procedures are inappropriate or are deemed not to reflect fair value are stated at fair value as determined in good faith by the Valuation Committee. The objective of any fair value pricing determination is to arrive at a price that could reasonably be expected from a current sale. Financial instruments fair valued by the Valuation Committee are primarily private placements, restricted securities, warrants, rights, and other securities that are not publicly traded.

Subject to oversight by the Board, the Valuation Committee regularly makes good faith judgments to establish and adjust the fair valuations of certain securities as events occur and circumstances warrant. For instance, in determining the fair value of an equity investment with limited market activity, such as a private placement or a thinly traded public company stock, the Valuation Committee considers a variety of factors, which may include, but are not limited to, the issuer’s business prospects, its financial standing and performance, recent investment transactions in the issuer, new rounds of financing, negotiated transactions of significant size between other investors in the company, relevant market valuations of peer companies, strategic events affecting the company, market liquidity for the issuer, and general economic conditions and events. In consultation with the investment and pricing teams, the Valuation Committee will determine an appropriate valuation technique based on available information, which may include both observable and unobservable inputs. The Valuation Committee typically will afford greatest weight to actual prices in arm’s length transactions, to the extent they represent orderly transactions between market participants, transaction information can be reliably obtained, and prices are deemed representative of fair value. However, the Valuation Committee may also consider other valuation methods such as market-based valuation multiples; a discount or premium from market value of a similar, freely traded security of the same issuer; or some combination. Fair value determinations are reviewed on a regular basis and updated as information becomes available, including actual purchase and sale transactions of the issue. Because any fair value determination involves a significant amount of judgment, there is a degree of subjectivity inherent in such pricing decisions, and fair value prices determined by the Valuation Committee could differ from those of other market participants. Depending on the relative significance of unobservable inputs, including the valuation technique(s) used, fair valued securities may be categorized in Level 2 or 3 of the fair value hierarchy.

Valuation Inputs On December 31, 2017, all of the fund’s financial instruments were classified as Level 1, based on the inputs used to determine their fair values. There were no material transfers between Levels 1 and 2 during the year ended December 31, 2017.

Consistent with its investment objective, the fund engages in the following practices to manage exposure to certain risks and/or to enhance performance. The investment objective, policies, program, and risk factors of the fund are described more fully in the fund’s prospectus and Statement of Additional Information.

Securities Lending The fund may lend its securities to approved borrowers to earn additional income. Its securities lending activities are administered by a lending agent in accordance with a securities lending agreement. Security loans generally do not have stated maturity dates, and the fund may recall a security at any time. The fund receives collateral in the form of cash or U.S. government securities, valued at 102% to 105% of the value of the securities on loan. Collateral is maintained over the life of the loan in an amount not less than the value of loaned securities; any additional collateral required due to changes in security values is delivered to the fund the next business day. Cash collateral is invested in accordance with investment guidelines approved by fund management. Additionally, the lending agent indemnifies the fund against losses resulting from borrower default. Although risk is mitigated by the collateral and indemnification, the fund could experience a delay in recovering its securities and a possible loss of income or value if the borrower fails to return the securities, collateral investments decline in value, and the lending agent fails to perform. Securities lending revenue consists of earnings on invested collateral and borrowing fees, net of any rebates to the borrower, compensation to the lending agent, and other administrative costs. In accordance with GAAP, investments made with cash collateral are reflected in the accompanying financial statements, but collateral received in the form of securities is not. At December 31, 2017, the value of loaned securities was $551,000 the value of cash collateral and related investments was $584,000.

Other Purchases and sales of portfolio securities other than short-term securities aggregated $1,702,000 and $1,879,000, respectively, for the year ended December 31, 2017.

No provision for federal income taxes is required since the fund intends to continue to qualify as a regulated investment company under Subchapter M of the Internal Revenue Code and distribute to shareholders all of its taxable income and gains. Distributions determined in accordance with federal income tax regulations may differ in amount or character from net investment income and realized gains for financial reporting purposes. Financial reporting records are adjusted for permanent book/tax differences to reflect tax character but are not adjusted for temporary differences.

The fund files U.S. federal, state, and local tax returns as required. The fund’s tax returns are subject to examination by the relevant tax authorities until expiration of the applicable statute of limitations, which is generally three years after the filing of the tax return but which can be extended to six years in certain circumstances. Tax returns for open years have incorporated no uncertain tax positions that require a provision for income taxes.

Distributions during the years ended December 31, 2017 and December 31, 2016, were characterized for tax purposes as follows:

At December 31, 2017, the tax-basis cost of investments, including derivatives, and components of net assets were as follows:

The difference between book-basis and tax-basis net unrealized appreciation (depreciation) is attributable to the deferral of losses from wash sales for tax purposes.

The fund is managed by T. Rowe Price Associates, Inc. (Price Associates), a wholly owned subsidiary of T. Rowe Price Group, Inc. (Price Group). The investment management agreement between the fund and Price Associates provides for an annual investment management fee equal to 0.12% of the fund’s average daily net assets. The fee is computed daily and paid monthly.

The Investor Class is subject to a contractual expense limitation through April 30, 2018. During the limitation period, Price Associates is required to waive its management fee or pay any expenses (excluding interest, expenses related to borrowings, taxes, brokerage, and other non-recurring expenses permitted by the investment management agreement) that would otherwise cause the class’s ratio of annualized total expenses to average net assets (expense ratio) to exceed its expense limitation of 0.32%. The class is required to repay Price Associates for expenses previously waived/paid to the extent the class’s net assets grow or expenses decline sufficiently to allow repayment without causing the class’s expense ratio (after the repayment is taken into account) to exceed both: (1) the expense limitation in place at the time such amounts were waived; and (2) the class’s current expense limitation. However, no repayment will be made more than three years after the date of a payment or waiver.

The I Class is also subject to an operating expense limitation (I Class limit) pursuant to which Price Associates is contractually required to pay all operating expenses of the I Class, excluding management fees, interest, expenses related to borrowings, taxes, brokerage, and other non-recurring expenses permitted by the investment management agreement, to the extent such operating expenses, on an annualized basis, exceed 0.05% of average net assets. This agreement will continue until April 30, 2018, and may be renewed, revised, or revoked only with approval of the fund’s Board. The I Class is required to repay Price Associates for expenses previously paid to the extent the class’s net assets grow or expenses decline sufficiently to allow repayment without causing the class’s operating expenses (after the repayment is taken into account) to exceed both: (1) the expense limitation in place at the time such amounts were paid; and (2) the class’s current expense limitation. However, no repayment will be made more than three years after the date of a payment or waiver.

Pursuant to these agreements, $234,000 of expenses were waived/paid by Price Associates during the year ended December 31, 2017. Including this amount, expenses previously waived/paid by Price Associates in the amount of $464,000 remain subject to repayment by the fund at December 31, 2017.

In addition, the fund has entered into service agreements with Price Associates and a wholly owned subsidiary of Price Associates (collectively, Price). Price Associates provides certain accounting and administrative services to the fund. T. Rowe Price Services, Inc. provides shareholder and administrative services in its capacity as the fund’s transfer and dividend-disbursing agent. For the year ended December 31, 2017, expenses incurred pursuant to these service agreements were $86,000 for Price Associates and less than $1,000 for T. Rowe Price Services, Inc. The total amount payable at period-end pursuant to these service agreements is reflected as Due to Affiliates in the accompanying financial statements.

The fund may invest its cash reserves in certain open-end management investment companies managed by Price Associates and considered affiliates of the fund: the T. Rowe Price Government Reserve Fund or the T. Rowe Price Treasury Reserve Fund, organized as money market funds, or the T. Rowe Price Short-Term Fund, a short-term bond fund (collectively, the Price Reserve Funds). The Price Reserve Funds are offered as short-term investment options to mutual funds, trusts, and other accounts managed by Price Associates or its affiliates and are not available for direct purchase by members of the public. Cash collateral from securities lending is invested in the T. Rowe Price Short-Term Fund. The Price Reserve Funds pay no investment management fees.

As of December 31, 2017, T. Rowe Price Group, Inc., or its wholly owned subsidiaries owned 475,000 shares of the Investor Class, representing 100% of the Investor Class’s net assets and 25,000 shares of the I Class, representing 100% of the I Class’s net assets.

The fund may participate in securities purchase and sale transactions with other funds or accounts advised by Price Associates (cross trades), in accordance with procedures adopted by the fund’s Board and Securities and Exchange Commission rules, which require, among other things, that such purchase and sale cross trades be effected at the independent current market price of the security. During the year ended December 31, 2017, the fund had no purchases or sales cross trades with other funds or accounts advised by Price Associates.

To the Board of Directors of T. Rowe Price Index Trust, Inc. and
Shareholders of T. Rowe Price Mid-Cap Index Fund

We have audited the accompanying statement of assets and liabilities, including the portfolio of investments, of T. Rowe Price Mid-Cap Index Fund (one of the funds constituting T. Rowe Price Index Trust, Inc., hereafter referred to as the “Fund”) as of December 31, 2017, the related statement of operations for the year ended December 31, 2017, the statement of changes in net assets for each of the two years in the period ended December 31, 2017, including the related notes, and the financial highlights for each of the three periods indicated therein (collectively referred to as the “financial statements”). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Fund as of December 31, 2017, the results of its operations for the year then ended, the changes in its net assets for each of the two years in the period ended December 31, 2017 and the financial highlights for each of the three periods indicated therein, in conformity with accounting principles generally accepted in the United States of America.

These financial statements are the responsibility of the Fund’s management. Our responsibility is to express an opinion on the Fund’s financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (“PCAOB”) and are required to be independent with respect to the Fund in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits of these financial statements in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud.

Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. Our procedures included confirmation of securities owned as of December 31, 2017 by correspondence with the custodian, transfer agent and brokers; when replies were not received from brokers, we performed other auditing procedures. We believe that our audits provide a reasonable basis for our opinion.

We have served as the auditor of one or more investment companies in the T. Rowe Price group of investment companies since 1973.

We are providing this information as required by the Internal Revenue Code. The amounts shown may differ from those elsewhere in this report because of differences between tax and financial reporting requirements.

For taxable non-corporate shareholders, $46,000 of the fund’s income represents qualified dividend income subject to a long-term capital gains tax rate of not greater than 20%.

For corporate shareholders, $40,000 of the fund’s income qualifies for the dividends-received deduction.

A description of the policies and procedures used by T. Rowe Price funds and portfolios to determine how to vote proxies relating to portfolio securities is available in each fund’s Statement of Additional Information. You may request this document by calling 1-800-225-5132 or by accessing the SEC’s website, sec.gov.

The description of our proxy voting policies and procedures is also available on our corporate website. To access it, please visit the following Web page:

Scroll down to the section near the bottom of the page that says, “Proxy Voting Policies.” Click on the Proxy Voting Policies link in the shaded box.

Each fund’s most recent annual proxy voting record is available on our website and through the SEC’s website. To access it through T. Rowe Price, visit the website location shown above, and scroll down to the section near the bottom of the page that says, “Proxy Voting Records.” Click on the Proxy Voting Records link in the shaded box.

The fund files a complete schedule of portfolio holdings with the Securities and Exchange Commission for the first and third quarters of each fiscal year on Form N-Q. The fund’s Form N-Q is available electronically on the SEC’s website (sec.gov); hard copies may be reviewed and copied at the SEC’s Public Reference Room, 100 F St. N.E., Washington, DC 20549. For more information on the Public Reference Room, call 1-800-SEC-0330.

Your fund is overseen by a Board of Directors (Board) that meets regularly to review a wide variety of matters affecting or potentially affecting the fund, including performance, investment programs, compliance matters, advisory fees and expenses, service providers, and business and regulatory affairs. The Board elects the fund’s officers, who are listed in the final table. At least 75% of the Board’s members are independent of T. Rowe Price Associates, Inc. (T. Rowe Price), and its affiliates; “inside” or “interested” directors are employees or officers of T. Rowe Price. The business address of each director and officer is 100 East Pratt Street, Baltimore, Maryland 21202. The Statement of Additional Information includes additional information about the fund directors and is available without charge by calling a T. Rowe Price representative at 1-800-638-5660.

The registrant has adopted a code of ethics, as defined in Item 2 of Form N-CSR, applicable to its principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions. A copy of this code of ethics is filed as an exhibit to this Form N-CSR. No substantive amendments were approved or waivers were granted to this code of ethics during the period covered by this report.

The registrant’s Board of Directors/Trustees has determined that Mr. Bruce W. Duncan qualifies as an audit committee financial expert, as defined in Item 3 of Form N-CSR. Mr. Duncan is considered independent for purposes of Item 3 of Form N-CSR.

(a) – (d) Aggregate fees billed for the last two fiscal years for professional services rendered to, or on behalf of, the registrant by the registrant’s principal accountant were as follows:

Audit fees include amounts related to the audit of the registrant’s annual financial statements and services normally provided by the accountant in connection with statutory and regulatory filings. Audit-related fees include amounts reasonably related to the performance of the audit of the registrant’s financial statements and specifically include the issuance of a report on internal controls and, if applicable, agreed-upon procedures related to fund acquisitions. Tax fees include amounts related to services for tax compliance, tax planning, and tax advice. The nature of these services specifically includes the review of distribution calculations and the preparation of Federal, state, and excise tax returns. All other fees include the registrant’s pro-rata share of amounts for agreed-upon procedures in conjunction with service contract approvals by the registrant’s Board of Directors/Trustees.

(e)(1) The registrant’s audit committee has adopted a policy whereby audit and non-audit services performed by the registrant’s principal accountant for the registrant, its investment adviser, and any entity controlling, controlled by, or under common control with the investment adviser that provides ongoing services to the registrant require pre-approval in advance at regularly scheduled audit committee meetings. If such a service is required between regularly scheduled audit committee meetings, pre-approval may be authorized by one audit committee member with ratification at the next scheduled audit committee meeting. Waiver of pre-approval for audit or non-audit services requiring fees of a de minimis amount is not permitted.

(2) No services included in (b) – (d) above were approved pursuant to paragraph (c)(7)(i)(C) of Rule 2-01 of Regulation S-X.

(f) Less than 50 percent of the hours expended on the principal accountant’s engagement to audit the registrant’s financial statements for the most recent fiscal year were attributed to work performed by persons other than the principal accountant’s full-time, permanent employees.

(g) The aggregate fees billed for the most recent fiscal year and the preceding fiscal year by the registrant’s principal accountant for non-audit services rendered to the registrant, its investment adviser, and any entity controlling, controlled by, or under common control with the investment adviser that provides ongoing services to the registrant were $2,169,000 and $2,146,000, respectively.

(h) All non-audit services rendered in (g) above were pre-approved by the registrant’s audit committee. Accordingly, these services were considered by the registrant’s audit committee in maintaining the principal accountant’s independence.

(a) Not applicable. The complete schedule of investments is included in Item 1 of this Form N-CSR.

Item 7. Disclosure of Proxy Voting Policies and Procedures for Closed-End Management Investment Companies.

Item 9. Purchases of Equity Securities by Closed-End Management Investment Company and Affiliated Purchasers.

(a) The registrant’s principal executive officer and principal financial officer have evaluated the registrant’s disclosure controls and procedures within 90 days of this filing and have concluded that the registrant’s disclosure controls and procedures were effective, as of that date, in ensuring that information required to be disclosed by the registrant in this Form N-CSR was recorded, processed, summarized, and reported timely.

(b) The registrant’s principal executive officer and principal financial officer are aware of no change in the registrant’s internal control over financial reporting that occurred during the registrant’s second fiscal quarter covered by this report that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting.

(a)(1) The registrant’s code of ethics pursuant to Item 2 of Form N-CSR is attached.

(2) Separate certifications by the registrant's principal executive officer and principal financial officer, pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 and required by Rule 30a-2(a) under the Investment Company Act of 1940, are attached.

(3) Written solicitation to repurchase securities issued by closed-end companies: not applicable.

(b) A certification by the registrant's principal executive officer and principal financial officer, pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 and required by Rule 30a-2(b) under the Investment Company Act of 1940, is attached.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

T. Rowe Price Index Trust, Inc.

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

		By	/s/ Edward C. Bernard
			Edward C. Bernard
			Principal Executive Officer

Date	February 20, 2018


		By	/s/ Catherine D. Mathews
			Catherine D. Mathews
			Principal Financial Officer

Date	February 20, 2018

●	$15,000 from short-term capital gains,

●	$175,000 from long-term capital gains, subject to a long-term capital gains tax rate of not greater than 20%

Independent Directors

Name
(Year of Birth)
Year Elected*
[Number of T. Rowe Price		Principal Occupation(s) and Directorships of Public Companies and
Portfolios Overseen]		Other Investment Companies During the Past Five Years

Bruce W. Duncan		Chief Executive Officer and Director (2009 to December 2016),
(1951)		Chairman of the Board (January 2016 to present), and President
2013		(2009 to September 2016), First Industrial Realty Trust, an owner
[191]		and operator of industrial properties; Chairman of the Board
		(2005 to September 2016) and Director (1999 to September
		2016), Starwood Hotels & Resorts, a hotel and leisure company;
		Director, Boston Properties (May 2016 to present); Director,
		Marriott International, Inc. (September 2016 to present)

Robert J. Gerrard, Jr.		Advisory Board Member, Pipeline Crisis/Winning Strategies, a
(1952)		collaborative working to improve opportunities for young African
2012		Americans (1997 to present)
[191]

Paul F. McBride		Advisory Board Member, Vizzia Technologies (2015 to present)
(1956)
2013
[191]

Cecilia E. Rouse, Ph.D.		Dean, Woodrow Wilson School (2012 to present); Professor and
(1963)		Researcher, Princeton University (1992 to present); Member of
2012		National Academy of Education (2010 to present); Director, MDRC,
[191]		a nonprofit education and social policy research organization (2011
		to present); Research Associate of Labor Studies Program (2011
		to 2015) and Board Member (2015 to present), National Bureau
		of Economic Research (2011 to present); Chair of Committee
		on the Status of Minority Groups in the Economic Profession
		(2012 to present); Vice President (2015 to present), American
		Economic Association

John G. Schreiber		Owner/President, Centaur Capital Partners, Inc., a real estate
(1946)		investment company (1991 to present); Cofounder, Partner, and
2001		Cochairman of the Investment Committee, Blackstone Real Estate
[191]		Advisors, L.P. (1992 to 2015); Director, General Growth Properties,
		Inc. (2010 to 2013); Director, Blackstone Mortgage Trust, a real
		estate finance company (2012 to 2016); Director and Chairman of
		the Board, Brixmor Property Group, Inc. (2013 to present); Director,
		Hilton Worldwide (2013 to present); Director, Hudson Pacific
		Properties (2014 to 2016)

Mark R. Tercek		President and Chief Executive Officer, The Nature Conservancy (2008
(1957)		to present)
2009
[191]

*Each independent director serves until retirement, resignation, or election of a successor.

Inside Directors

Name
(Year of Birth)
Year Elected*
[Number of T. Rowe Price		Principal Occupation(s) and Directorships of Public Companies and
Portfolios Overseen]		Other Investment Companies During the Past Five Years

Edward C. Bernard		Director and Vice President, T. Rowe Price; Vice Chairman of the
(1956)		Board, Director, and Vice President, T. Rowe Price Group, Inc.;
2006		Chairman of the Board, Director, and Vice President, T. Rowe Price
[191]		Investment Services, Inc., and T. Rowe Price Services, Inc.; Chairman
		of the Board and Director, T. Rowe Price Retirement Plan Services,
		Inc.; Chairman of the Board, Chief Executive Officer, Director, and
		President, T. Rowe Price International and T. Rowe Price Trust
		Company; Chairman of the Board, all funds

Robert W. Sharps, CFA,		Vice President, T. Rowe Price, T. Rowe Price Group, Inc., and T. Rowe
CPA**		Price Trust Company
(1971)
2017
[135]

*Each inside director serves until retirement, resignation, or election of a successor.
**Effective April 1, 2017, Brian C. Rogers was replaced by Robert W. Sharps as an inside director of certain Price Funds.

Officers

Name (Year of Birth)
Position Held With Index Trust		Principal Occupation(s)

E. Frederick Bair, CFA, CPA (1969)		Vice President, T. Rowe Price, T. Rowe Price
Vice President		Group, Inc., and T. Rowe Price Trust Company

Darrell N. Braman (1963)		Vice President, Price Hong Kong, Price
Vice President and Secretary		Singapore, T. Rowe Price, T. Rowe Price Group,
		Inc., T. Rowe Price International, T. Rowe Price
		Investment Services, Inc., and T. Rowe Price
		Services, Inc.

John R. Gilner (1961)		Chief Compliance Officer and Vice President,
Chief Compliance Officer		T. Rowe Price; Vice President, T. Rowe Price
		Group, Inc., and T. Rowe Price Investment
		Services, Inc.

Paul J. Krug, CPA (1964)		Vice President, T. Rowe Price, T. Rowe Price
Vice President		Group, Inc., and T. Rowe Price Trust Company

Catherine D. Mathews (1963)		Vice President, T. Rowe Price, T. Rowe Price
Treasurer and Vice President		Group, Inc., and T. Rowe Price Trust Company

David Oestreicher (1967)		Director, Vice President, and Secretary, T. Rowe
Vice President		Price Investment Services, Inc., T. Rowe
		Price Retirement Plan Services, Inc., T. Rowe
		Price Services, Inc., and T. Rowe Price Trust
		Company; Chief Legal Officer, Vice President,
		and Secretary, T. Rowe Price Group, Inc.; Vice
		President and Secretary, T. Rowe Price and
		T. Rowe Price International; Vice President,
		Price Hong Kong and Price Singapore

John W. Ratzesberger (1975)		Vice President, T. Rowe Price, T. Rowe Price
Vice President		Group, Inc., and T. Rowe Price Trust Company;
		formerly, North American Head of Listed
		Derivatives Operation, Morgan Stanley (to 2013)

Shannon H. Rauser (1987)		Employee, T. Rowe Price
Assistant Secretary

Neil Smith (1972)		Vice President, Price Hong Kong, Price
Vice President		Singapore, T. Rowe Price Group, Inc., and
		T. Rowe Price International

Craig A. Thiese (1975)		Vice President, T. Rowe Price and T. Rowe Price
Vice President		Group, Inc.

Ken D. Uematsu, CFA (1969)		Vice President, T. Rowe Price, T. Rowe Price
President		Group, Inc., and T. Rowe Price Trust Company

Megan Warren (1968)		Vice President, T. Rowe Price, T. Rowe Price
Vice President		Group, Inc., T. Rowe Price Retirement Plan
		Services, Inc., T. Rowe Price Services, Inc.,
		and T. Rowe Price Trust Company; formerly,
		Executive Director, JP Morgan Chase (to 2017)

Michael T. Wehn (1984)		Vice President, T. Rowe Price
Vice President

Unless otherwise noted, officers have been employees of T. Rowe Price or T. Rowe Price International for at least 5 years.

/s/ Edward C. Bernard

Edward C. Bernard

Principal Executive Officer

February 20, 2018