X0202 3 2007-07-30 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 Common Stock 7500 D Incentive Stock Option (right to buy) 7.250 2017-03-09 Common Stock 22500 D Incentive Stock Option (right to buy) 10.00 2015-02-09 Common Stock 20834 D Non-Qualified Stock Option (right to buy) 7.250 2017-03-09 Common Stock 17500 D Non-Qualified Stock Option (right to buy) 10.00 2015-02-09 Common Stock 9166 D The option vests and becomes exercisable with respect to 1/4th of the shares one year after the date of grant, and thereafter continues to vest and become exercisable as to 1/48th of the shares each month thereafter (with the shares fully vested on the 4th anniversary of the date of grant). 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