Vanguard PRIMECAP Fund

Supplement to the Prospectus and Summary Prospectus Dated January 26, 2012

Prospectus and Summary Prospectus Text Changes

The following text replaces similar text:

Investment Advisor
PRIMECAP Management Company

Portfolio Managers

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.

Prospectus Text Changes

In the More on the Fund section, under the heading “Investment Advisor,” the following text replaces similar text:

The managers primarily responsible for the day-to-day management of the Fund are:

Theo A. Kolokotrones, Vice Chairman of PRIMECAP. He has worked in investment management since 1970; has managed assets since 1979; has been with PRIMECAP since 1983; and has co-managed the Fund since 1985. Education: B.A., University of Chicago; M.B.A., Harvard Business School.

(over, please)

Joel P. Fried, President of PRIMECAP. He has worked in investment management since 1985; has been with PRIMECAP since 1986; has managed assets since 1987; and has co-managed the Fund since 1988. Education: B.S., University of California, Los Angeles; M.B.A., Anderson Graduate School of Business, University of California, Los Angeles.

Mitchell J. Milias, Chairman of PRIMECAP. He has worked in investment management since 1964; has managed assets since 1967; has been with PRIMECAP since 1983; and has co-managed the Fund since 2002. Education: B.S., Stanford University; M.B.A., Harvard Business School.

Alfred W. Mordecai, Executive Vice President of PRIMECAP. He has worked in investment management and has been with PRIMECAP since 1997; has managed assets since 1999; and has co-managed the Fund since 1999. Education: B.S.E., Duke University; M.E.A., Virginia Polytechnic Institute and State University; M.B.A., Harvard Business School.

M. Mohsin Ansari, Senior Vice President of PRIMECAP. He has worked in investment management and has been with PRIMECAP since 2000; has managed assets since 2007; and has co-managed the Fund since 2007. Education: B.A., Colgate University; B.S., Washington University; M.B.A., Harvard Business School.

Each of these five individuals manages a portion of the Fund autonomously; there is no decision-making by committee. A small portion of the Fund’s assets is managed by individuals in PRIMECAP’s research department.

The Statement of Additional Information provides information about each portfolio manager’s compensation, other accounts under management, and ownership of shares of the Fund.

© 2012 The Vanguard Group, Inc. All rights reserved.
Vanguard Marketing Corporation, Distributor.	PS 59A 042012

Vanguard Chester Funds

Supplement to the Statement of Additional Information Dated January 26, 2012

Change to Vanguard PRIMECAP Fund

The first paragraph under the heading “I. Vanguard PRIMECAP Fund” in the Investment Advisory Services section is
replaced with the following:

PRIMECAP Management Company (PRIMECAP), an investment advisory services firm founded in 1983, is a California
corporation whose outstanding shares are owned by its directors and officers. The directors of the corporation and the
offices they currently hold are: Mitchell J. Milias, Chairman; Theo A. Kolokotrones, Vice Chairman; Joel P. Fried,
President; and Alfred W. Mordecai, Executive Vice President. PRIMECAP provides investment advisory services to
endowment funds, employee benefits plans, and foundations unrelated to Vanguard.

Under the same heading, the paragraph under the subheading “A. Other Accounts Managed” is replaced with the following:

Theo A. Kolokotrones, Joel P. Fried, Mitchell J. Milias, Alfred W. Mordecai, and M. Mohsin Ansari jointly manage the
PRIMECAP Fund; as of September 30, 2011, the Fund held assets of $27.8 billion. As of September 30, 2011, each
manager (except Mr. Milias and Mr. Ansari) also jointly managed six other registered investment companies with total
assets of $14.8 billion (none of which had advisory fees based on account performance). Mr. Kolokotrones, Mr. Fried, Mr.
Mordecai, and Mr. Ansari also jointly managed one other pooled investment vehicle with total assets of $741.5 million
(advisory fee not based on account performance). As of September 30, 2011, the managers also individually managed
other accounts as follows: Mr. Kolokotrones, 36 accounts with total assets of $17.6 billion; Mr. Fried, 29 accounts with
total assets of $17.6 billion; Mr. Mordecai, 28 other accounts with total assets of $17.6 billion; Mr. Milias, 45 accounts
with total assets of $17.7 billion; and Mr. Ansari, ten accounts with total assets of $13.1 billion (none of which had
advisory fees based on account performance). As of September 30, 2011, Mr. Milias also jointly managed four other
registered investment companies with total assets of $7.1 billion (none of which had advisory fees based on account
performance). As of September 30, 2011, Mr. Ansari also jointly managed three other registered investment companies
with total assets of $11.4 billion and one other pooled investment vehicle with total assets of $741.5 million (none of
which had advisory fees based on account performance).

Also under the same heading, the paragraph under the subheading “D. Ownership of Securities” is replaced with
the following:

As of September 30, 2011, Mr. Kolokotrones, Mr. Fried, Mr. Mordecai, and Mr. Milias each owned shares of Vanguard
PRIMECAP Fund in an amount exceeding $1 million; and Mr. Ansari owned shares of the Fund within the $100,001–
$500,000 range.

© 2012 The Vanguard Group, Inc. All rights reserved.
Vanguard Marketing Corporation, Distributor.	SAI 059A 042012