Exhibit 99.1

THE ADVISORY BOARD COMPANY

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

Each of the undersigned hereby certifies, in his capacity as an officer of The Advisory Board Company (the “Company”), for purposes of 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

• the Quarterly Report of the Company on Form 10-Q for the period ended December 31, 2002 fully complies with the requirements of Section 13(a) of the Securities Exchange Act of 1934; and

• the information contained in such report fairly presents, in all material respects, the financial condition and results of operation of the Company.

/s/ Frank J. Williams                       
Frank J. Williams
Chief Executive Officer (Principal
Executive
Officer) and Director

/s/ David L. Felsenthal                  
David L. Felsenthal
Chief Financial Officer (Principal
Financial and
Accounting Officer), Secretary and
Treasurer

Dated: February 14, 2003