Ownership Submission
FORM 3
 UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
OMB APPROVAL
OMB Number: 3235-0104
Expires: January 31, 2005
Estimated average burden hours per response... 0.5

(Print or Type Responses)
1. Name and Address of Reporting Person *
  Riolo John
 2. Date of Event Requiring Statement (Month/Day/Year)
07/30/2007		 3. Issuer Name and Ticker or Trading Symbol
DEXCOM INC [DXCM]
(Last)
(First)
(Middle)
C/O DEXCOM, INC., 5555 OBERLIN DRIVE		 4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
VP of Quality Assurance
 5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

SAN DIEGO, CA 92121		 6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Beneficially Owned
1.Title of Security
(Instr. 4)		 2. Amount of Securities Beneficially Owned
(Instr. 4)		 3. Ownership Form: Direct (D) or Indirect (I)
(Instr. 5)		 4. Nature of Indirect Beneficial Ownership
(Instr. 5)
Common Stock 7,500
D
 

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 4)		 2. Date Exercisable and Expiration Date
(Month/Day/Year)		 3. Title and Amount of Securities Underlying Derivative Security
(Instr. 4)		 4. Conversion or Exercise Price of Derivative Security 5. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 5)		 6. Nature of Indirect Beneficial Ownership
(Instr. 5)
Date Exercisable Expiration Date Title Amount or Number of Shares
Incentive Stock Option (right to buy)   (1) 03/09/2017 Common Stock 22,500 $ 7.25 D  
Incentive Stock Option (right to buy)   (1) 02/09/2015 Common Stock 20,834 $ 10 D  
Non-Qualified Stock Option (right to buy)   (1) 03/09/2017 Common Stock 17,500 $ 7.25 D  
Non-Qualified Stock Option (right to buy)   (1) 02/09/2015 Common Stock 9,166 $ 10 D  

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
Riolo John
C/O DEXCOM, INC.
5555 OBERLIN DRIVE
SAN DIEGO, CA 92121		       VP of Quality Assurance  

Signatures

/s/ By: Jess Roper for John Riolo 08/06/2007
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 5(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) 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).
 
Remarks:
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

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, See Instruction 6 for procedure.

Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB number.