Explanation of Responses:

(1)  The stockholder is Warburg Pincus Ventures, L.P. ("Ventures"). Ventures
     beneficially owns 8,526,852 shares of common stock ("Common Stock") of
     Kyphon Inc. (the "Issuer"). The sole general partner of Ventures is Warburg
     Pincus Partners LLC, a New York limited liability company ("WPP LLC") and a
     subsidiary of Warburg Pincus & Co. ("WP"). Warburg Pincus LLC (formerly
     E.M. Warburg Pincus & Co., LLC), a New York limited liability company ("WP
     LLC"), manages Ventures. By reason of the provisions of Rule 16a-1 of the
     Exchange Act, WPP LLC, WP and WP LLC may be deemed to be the beneficial
     owners of the Common Stock held by Ventures, although WPP LLC, WP and WP
     LLC disclaim beneficial ownership of the Common Stock except to the extent
     of any indirect pecuniary interest therein. Ms. Weatherman, a director of
     the Issuer, is a general partner of WP and a member of WP LLC. As such, Ms
     Weatherman may be deemed to have an indirect pecuniary interest (within the
     meaning of Rule 16a-1 of the Exchange Act) in an indeterminate portion of
     the shares beneficially owned by Ventures, WP LLC, WP and WPP LLC. Ms.
     Weatherman disclaims beneficial ownership of such shares except to the
     extent of any indirect pecuniary interest therein.

(2)  On May 26, 2005, Ventures distributed an aggregate of 2,021,998 shares of
     Common Stock to its partners.

(3)  Price not applicable.