X0202 4 2007-08-02 0 0001093557 DEXCOM INC DXCM 0001408994 Riolo John C/O DEXCOM, INC. 5555 OBERLIN DRIVE SAN DIEGO CA 92121 0 1 0 0 VP of Quality Assurance Incentive Stock Option (right to buy) 7.79 2007-08-02 4 A 0 14323 A 2017-08-02 Common Stock 14323 14323 D Non-Qualified Stock Option (right to buy) 7.790 2007-08-02 4 A 0 35677 A 2017-08-02 Common Stock 35677 35677 D The option vests and becomes exercisable as to 1/48th each month beginning one month following the date of grant and become fully vested on the 48th month anniversary of the date of grant. Not applicable. CONFIRMING STATEMENT This Statement confirms that the undersigned, John Riolo, has authorized and designated Nooshin Hussainy, Jess Roper, and Steven R. Pacelli to execute and file on the undersigned's behalf all Forms 3, 4, and 5 (including any amendments thereto) that the undersigned may be required to file with the U.S. Securities and Exchange Commission as a result of the undersigned's ownership of or transactions in securities of DexCom, Inc. The authority of Nooshin Hussainy, Jess Roper, and Steve R. Pacelli under this Statement shall continue until the undersigned is no longer required to file Forms 3, 4, and 5 with regard to the undersigned's ownership of or transactions in securities of DexCom, Inc., unless earlier revoked in writing. The undersigned acknowledges that Nooshin Hussainy, Jess Roper, and Steven R. Pacelli are not assuming any of the undersigned's responsibilities to comply with Section 16 of the Securities Exchange Act of 1934. Date: Aug 2, 2007 /s/ JOHN RIOLO John Riolo /s/ By: Jess Roper for John Riolo 2007-08-06