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
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(Print or Type Responses)
1. Name and Address of Reporting Person *
  LISTER JOHN
 2. Date of Event Requiring Statement (Month/Day/Year)
05/19/2009		 3. Issuer Name and Ticker or Trading Symbol
DEXCOM INC [DXCM]
(Last)
(First)
(Middle)
C/O DEXCOM, INC., 6340 SEQUENCE DRIVE		 4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
VP, Legal Affairs
 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 1,500
D
 

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
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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) 01/13/2018 Common Stock 50,000 $ 8.85 D  
Non-Qualified Stock Option (Right to Buy)   (1) 05/18/2018 Common Stock 7,500 $ 7.63 D  
Non-Qualified Stock Option (Right to Buy)   (1) 12/10/2018 Common Stock 12,500 $ 3.19 D  

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
LISTER JOHN
C/O DEXCOM, INC.
6340 SEQUENCE DRIVE
SAN DIEGO, CA 92121		       VP, Legal Affairs  

Signatures

/s/ John Lister 05/22/2009
**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 Lister, has authorized and designated Jess Roper and Steven 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 Jess Roper and Steven 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 Jess Roper and Steven Pacelli are not assuming any of the undersigned's responsibilities to comply with Section 16 of the Securities Exchange Act of 1934.
Date:  May 20, 2008
/s/ JOHN LISTER
John Lister

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