Vanguard PRIMECAP Fund

Summary Prospectus

January 26, 2012

Investor Shares & Admiral™ Shares

Vanguard PRIMECAP Fund Investor Shares (VPMCX)

Vanguard PRIMECAP Fund Admiral Shares (VPMAX)

The Fund’s statutory Prospectus and Statement of Additional Information dated

January 26, 2012, are incorporated into and made part of this Summary

Prospectus by reference.

Before you invest, you may want to review the Fund’s Prospectus, which

contains more information about the Fund and its risks. You can find

the Fund’s Prospectus and other information about the Fund online at

www.vanguard.com/prospectus. You can also get this information at no

cost by calling 800-662-7447 or by sending an e-mail request to

online@vanguard.com.

The Securities and Exchange Commission (SEC) has not approved or disapproved these securities or

passed upon the adequacy of this prospectus. Any representation to the contrary is a criminal offense.

Investment Objective

The Fund seeks to provide long-term capital appreciation.

Fees and Expenses

The following table describes the fees and expenses you may pay if you buy and hold Investor Shares or Admiral Shares of the Fund.

Shareholder Fees
(Fees paid directly from your investment)
	Investor Shares	Admiral Shares
Sales Charge (Load) Imposed on Purchases	None	None
Purchase Fee	None	None
Sales Charge (Load) Imposed on Reinvested Dividends	None	None
Redemption Fee (on shares held less than one year)	1%	1%
Account Service Fee (for fund account balances below $10,000)	$20/year	$20/year

Annual Fund Operating Expenses
(Expenses that you pay each year as a percentage of the value of your investment)
	Investor Shares	Admiral Shares
Management Expenses	0.43%	0.34%
12b-1 Distribution Fee	None	None
Other Expenses	0.02%	0.02%
Total Annual Fund Operating Expenses	0.45%	0.36%

Examples

The following examples are intended to help you compare the cost of investing in the Fund’s Investor Shares or Admiral Shares with the cost of investing in other mutual funds. They illustrate the hypothetical expenses that you would incur over various periods if you invest $10,000 in the Fund’s shares. These examples assume that the Shares provide a return of 5% a year and that operating expenses remain as stated in the preceding table. The results apply whether or not you redeem your investment at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	1 Year	3 Years	5 Years	10 Years
Investor Shares	$46	$144	$252	$567
Admiral Shares	$37	$116	$202	$456

1

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells
securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate
higher transaction costs and may result in more taxes when Fund shares are held in a
taxable account. These costs, which are not reflected in annual fund operating
expenses or in the previous expense examples, reduce the Fund’s performance.
During the most recent fiscal year, the Fund’s portfolio turnover rate was 8%.

Primary Investment Strategies
The Fund invests in stocks considered to have above-average earnings growth
potential that is not reflected in their current market prices. The Fund’s portfolio
consists predominantly of large- and mid-capitalization stocks.

Primary Risks
An investment in the Fund could lose money over short or even long periods. You should
expect the Fund’s share price and total return to fluctuate within a wide range, like the
fluctuations of the overall stock market. The Fund’s performance could be hurt by:

• Stock market risk, which is the chance that stock prices overall will decline. Stock
markets tend to move in cycles, with periods of rising prices and periods of falling prices.

• Asset concentration risk, which is the chance that the Fund’s performance may be
adversely affected by the poor performance of relatively few stocks as compared with
other mutual funds. The Fund may concentrate a large portion of its assets in relatively
few holdings within the universe of undervalued stocks. As a result, the volatility
experienced by the Fund may be greater than the overall volatility of the stock market.

• Investment style risk, which is the chance that returns from large- and mid-
capitalization growth stocks will trail returns from the overall stock market. Historically,
mid-cap stocks have been more volatile in price than the large-cap stocks that
dominate the overall market, and they often perform quite differently.

• Manager risk, which is the chance that poor security selection or focus on securities in
a particular sector, category, or group of companies will cause the Fund to underperform
relevant benchmarks or other funds with a similar investment objective.

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

2

Annual Total Returns
The following bar chart and table are intended to help you understand the risks of
investing in the Fund. The bar chart shows how the performance of the Fund‘s
Investor Shares has varied from one calendar year to another over the periods shown.
The table shows how the average annual total returns of the share classes presented
compare with those of a relevant market index, which has investment characteristics
similar to those of the Fund. Keep in mind that the Fund’s past performance (before
and after taxes) does not indicate how the Fund will perform in the future. Updated
performance information is available on our website at vanguard.com/performance or
by calling Vanguard toll-free at 800-662-7447.

During the periods shown in the bar chart, the highest return for a calendar quarter
was 16.88% (quarter ended June 30, 2003), and the lowest return for a quarter was
–22.40% (quarter ended December 31, 2008).

Average Annual Total Returns for Periods Ended December 31, 2011
	1 Year	5 Years	10 Years
Vanguard PRIMECAP Fund Investor Shares
Return Before Taxes	–1.84%	2.34%	5.34%
Return After Taxes on Distributions	–2.49	1.67	4.80
Return After Taxes on Distributions and Sale of Fund Shares	–0.36	1.92	4.59
Vanguard PRIMECAP Fund Admiral Shares
Return Before Taxes	–1.77%	2.45%	5.47%
Standard & Poor's 500 Index
(reflects no deduction for fees, expenses, or taxes)	2.11%	–0.25%	2.92%

3

Actual after-tax returns depend on your tax situation and may differ from those shown
in the preceding table. When after-tax returns are calculated, it is assumed that the
shareholder was in the highest individual federal marginal income tax bracket at the
time of each distribution of income or capital gains or upon redemption. State and
local income taxes are not reflected in the calculations. Please note that after-tax
returns are shown only for the Investor Shares and may differ for each share class.
After-tax returns are not relevant for a shareholder who holds fund shares in a tax-
deferred account, such as an individual retirement account or a 401(k) plan. Also,
figures captioned Return After Taxes on Distributions and Sale of Fund Shares will be
higher than other figures for the same period if a capital loss occurs upon redemption
and results in an assumed tax deduction for the shareholder.

Investment Advisor
PRIMECAP Management Company

Portfolio Managers

Howard B. Schow, Chairman Emeritus of PRIMECAP. He has co-managed the Fund
since 1984.

Theo A. Kolokotrones, Vice Chairman of PRIMECAP. He has co-managed the Fund
since 1985.

Joel P. Fried, President of PRIMECAP. He has co-managed the Fund since 1988.

Mitchell J. Milias, Chairman of PRIMECAP. He has co-managed the Fund since 2002.

Alfred W. Mordecai, Executive Vice President of PRIMECAP. He has co-managed the
Fund since 1999.

M. Mohsin Ansari, Senior Vice President of PRIMECAP. He has co-managed the Fund
since 2007.

4

Purchase and Sale of Fund Shares
You may purchase or redeem shares online through our website (vanguard.com), by
mail (The Vanguard Group, P.O. Box 1110, Valley Forge, PA 19482-1110), or by telephone
(800-662-2739). The following table provides the Fund’s minimum initial and subsequent
investment requirements.

Account Minimums	Investor Shares	Admiral Shares
To open and maintain an account	$3,000	$50,000
To add to an existing account	Generally $100 (other than	Generally $100 (other than
	by Automatic Investment	by Automatic Investment
	Plan, which has no	Plan, which has no
	established minimum)	established minimum)

Tax Information
The Fund’s distributions may be taxable as ordinary income or capital gain.

Payments to Financial Intermediaries
The Fund and its investment advisor do not pay financial intermediaries for sales of
Fund shares.

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Vanguard PRIMECAP Fund Investor Shares—Fund Number 59
Vanguard PRIMECAP Fund Admiral Shares—Fund Number 559

© 2012 The Vanguard Group, Inc. All rights reserved.
Vanguard Marketing Corporation, Distributor.

SP 59 012012