QuickLinks -- Click here to rapidly navigate through this document



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


FORM 10-K/A
Amendment No. 1

(Mark One)  

ý

ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

FOR THE FISCAL YEAR ENDED DECEMBER 27, 2003

OR

o

TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

FOR THE TRANSITION PERIOD FROM                                TO                                 

Commission File No. 333-92383


CHARLES RIVER LABORATORIES INTERNATIONAL, INC.
(Exact Name of Registrant as Specified in Its Charter)

Delaware
(State or Other Jurisdiction of
Incorporation or Organization)
  06-1397316
(I.R.S. Employer
Identification No.)

251 Ballardvale Street
Wilmington, Massachusetts

(Address of Principal Executive Offices)

 

01887
(Zip Code)

(Registrant's telephone number, including area code): (978) 658-6000

Securities registered pursuant to Section 12(b) of the Act:

Title of each class
  Name of each exchange on which registered
Common Stock, $0.01 par value   New York Stock Exchange

Securities registered pursuant to Section 12(g) of the Act: None

        Indicate by check mark whether the Registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ý    No o

        Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of the Registrant's knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. o

        Indicate by check mark whether the Registrant is an accelerated filer (as defined in Exchange Act Rule 12b-2). Yes ý    No o

        On June 28, 2003, the aggregate market value of the Registrant's voting common stock held by non-affiliates of the Registrant was approximately $1,453,176,300.

        As of March 3, 2004, there were outstanding 46,074,943 shares of the Registrant's common stock, $0.01 par value per share.

DOCUMENTS INCORPORATED BY REFERENCE

        Portions of the Registrant's Definitive Proxy Statement for its 2004 Annual Meeting of Stockholders scheduled to be held on May 12, 2004 (the 2004 Proxy Statement), which will be filed with the Securities and Exchange Commission not later than 120 days after December 27, 2003, are incorporated by reference into Part III of this Annual Report on Form 10-K. With the exception of the portions of the 2004 Proxy Statement expressly incorporated into this Annual Report on Form 10-K by reference, such document shall not be deemed filed as part of this Form 10-K.





EXPLANATORY NOTE

        Charles River Laboratories International, Inc. is filing this amendment to Form 10-K for the year ended December 27, 2003, filed with the Securities and Exchange Commission on March 10, 2004, to amend the cover sheet by removing the check mark from the box relating to Item 405 of Regulation S-K. Otherwise, the Form 10-K is not amended in any way by this Amendment No. 1.

1



SIGNATURES

        Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

    CHARLES RIVER LABORATORIES INTERNATIONAL, INC.

Date: April 8, 2004

 

By:

/s/  
THOMAS F. ACKERMAN      
Thomas F. Ackerman
Senior Vice President and
Chief Financial Officer

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

Signatures

  Title

  Date


 

 

 

 

 

 

 
By:   /s/  JAMES C. FOSTER      
James C. Foster
  President, Chief Executive Officer and Chairman   April 8, 2004

By:

 

/s/  
THOMAS F. ACKERMAN      
Thomas F. Ackerman

 

Senior Vice President and Chief Financial Officer

 

April 8, 2004

By:

 

/s/  
ROBERT CAWTHORN      
Robert Cawthorn

 

Director

 

April 8, 2004

By:

 

/s/  
STEPHEN D. CHUBB      
Stephen D. Chubb

 

Director

 

April 8, 2004

By:

 

/s/  
GEORGE E. MASSARO      
George E. Massaro

 

Director

 

April 8, 2004

By:

 

/s/  
GEORGE M. MILNE      
George M. Milne

 

Director

 

April 8, 2004

By:

 

/s/  
DOUGLAS E. ROGERS      
Douglas E. Rogers

 

Director

 

April 8, 2004

By:

 

/s/  
SAMUEL O. THIER      
Samuel O. Thier

 

Director

 

April 8, 2004

By:

 

/s/  
WILLIAM H. WALTRIP      
William H. Waltrip

 

Director

 

April 8, 2004

2



EXHIBIT INDEX

Exhibit
Index

  Description
31.1*   Rule 13a-14(a)/15d-14(a) Certification of the Chief Executive Officer
31.2*   Rule 13a-14(a)/15d-14(a) Certification of the Chief Financial Officer
32.1*   Section 1350 Certification of the Chief Executive Officer
32.2*   Section 1350 Certification of the Chief Financial Officer

*
Filed herewith

3




QuickLinks

EXPLANATORY NOTE
SIGNATURES
EXHIBIT INDEX

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 31.1


CERTIFICATION PURSUANT TO
SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002
AND RULE 13a-14(a)/15d-14(a) OF THE EXCHANGE ACT OF 1934

        I, James C. Foster, Chief Executive Officer of Charles River Laboratories International, Inc. (the Company) certify that:


Dated: April 8, 2004   /s/  JAMES C. FOSTER      
James C. Foster
Chairman, Chief Executive Officer and President
Charles River Laboratories International, Inc.



QuickLinks

CERTIFICATION PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002 AND RULE 13a-14(a)/15d-14(a) OF THE EXCHANGE ACT OF 1934

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 31.2


CERTIFICATION PURSUANT TO
SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002
AND RULE 13a-14(a)/15d-14(a) OF THE EXCHANGE ACT OF 1934

        I, Thomas F. Ackerman, Senior Vice President and Chief Financial Officer of Charles River Laboratories International, Inc. (the Company) certify that:


Dated: April 8, 2004   /s/  THOMAS F. ACKERMAN      
Thomas F. Ackerman
Senior Vice President and Chief Financial Officer
Charles River Laboratories International, Inc.



QuickLinks

CERTIFICATION PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002 AND RULE 13a-14(a)/15d-14(a) OF THE EXCHANGE ACT OF 1934

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 32.1


CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,
AS ADOPTED PURSUANT TO
SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

        In connection with Amendment No. 1 to the Annual Report on Form 10-K/A for the period ending December 27, 2003 of Charles River Laboratories International, Inc. (the "Company") as filed with the Securities and Exchange Commission on the date hereof (the "Report"), the undersigned, James C. Foster, Chairman, Chief Executive Officer and President of the Company, hereby certifies, to the best of his knowledge and pursuant to 18 U.S.C. Section 1350, that:

        (1)   the Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

        (2)   the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Dated: April 8, 2004   /s/  JAMES C. FOSTER      
James C. Foster
Chairman, Chief Executive Officer and President
Charles River Laboratories International, Inc.



QuickLinks

CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350, AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 32.2


CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,
AS ADOPTED PURSUANT TO
SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

        In connection with Amendment No. 1 to the Annual Report on Form 10-K/A for the period ending December 27, 2003 of Charles River Laboratories International, Inc. (the "Company") as filed with the Securities and Exchange Commission on the date hereof (the "Report"), the undersigned, Chief Financial Officer of the Company, hereby certifies, to the best of his knowledge and pursuant to 18 U.S.C. Section 1350, that:

        (1)   the Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

        (2)   the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Dated: April 8, 2004   /s/  THOMAS F. ACKERMAN      
Thomas F. Ackerman
Senior Vice President and Chief Financial Officer
Charles River Laboratories International, Inc.



QuickLinks

CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350, AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002