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As filed with the Securities and Exchange Commission on April 27, 2006

Registration Number 333-          

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

DexCom, Inc.
(Exact name of Registrant as specified in its charter)

Delaware
(State or other jurisdiction of
incorporation or organization)		 3841
(Primary Standard Industrial
Classification Code Number)		 33-0857544
(I.R.S. Employer
Identification Number)

DexCom, Inc.
5555 Oberlin Drive
San Diego, California 92121
(858) 200-0200
(Address, including zip code, and telephone number, including area code, of Registrant's principal executive offices)

Andrew P. Rasdal
President and Chief Executive Officer
DexCom, Inc.
5555 Oberlin Drive
San Diego, California 92121
(858) 200-0200
 (Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Gordon K. Davidson, Esq.
Robert A. Freedman, Esq.
Scott J. Leichtner, Esq.
FENWICK & WEST LLP
801 California Street
Mountain View, California 94041
(650) 988-8500		 Charles Ruck, Esq.
Shayne Kennedy, Esq.
LATHAM & WATKINS LLP
650 Town Center Drive, 20th Floor
Costa Mesa, California 92626
(714) 540-1235

        Approximate date of commencement of proposed sale to the public:    As soon as practicable after the effective date of this Registration Statement.

        If any of the securities being registered on this form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box. o

        If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ý 333-133032

        If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

        If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

CALCULATION OF REGISTRATION FEE

Title of Each Class of
Securities to be Registered
   Amount to be
Registered
   Proposed Maximum
Offering Price
Per Share
   Proposed Maximum
Aggregate
Offering Price
   Amount of
Registration Fee
Common Stock, par value $0.001 per share(1)   57,500(2)(3)   $24.00(4)   $1,380,000   $148
(1)
This registration statement also covers rights to purchase shares of the Registrant's Series A junior participating preferred stock (the "Rights") that are attached to all shares of the Registrant's common stock. Until the occurrence of certain prescribed events, the Rights are not exercisable, are evidenced by the certificates for common stock and will be transferable along with and only with the common stock. The value attributable to the Rights, if any, is reflected in the value of the common stock.
(2)
The 57,500 shares being registered under this Registration Statement are in addition to the 5,442,375 shares registered pursuant to the Registration Statement on Form S-1 (File 333-133032), as amended.
(3)
Includes 7,500 shares subject to the underwriters' over-allotment option.
(4)
Based on the public offering price of the shares.

        This Registration Statement shall become effective upon filing with the Commission in accordance with Rule 462(b) under the Securities Act of 1933 as amended.


EXPLANATORY NOTE AND INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

        This Registration Statement on Form S-1 is being filed with respect to the registration of additional shares of common stock, par value $0.001 per share, of DexCom, Inc., a Delaware corporation, pursuant to Rule 462(b) under the Securities Act of 1933. This Registration Statement includes the registration statement facing page, this page, the signature pages, an exhibit index, an opinion of counsel regarding the legality of the securities being registered and a related consent and an accountant's consent. This Registration Statement relates to the Registrant's Registration Statement on Form S-1, as amended (Registration No. 333-133032), initially filed by the Registrant on April 6, 2006 and declared effective by the Securities and Exchange Commission on April 26, 2006. The Registrant is filing this Registration Statement for the sole purpose of increasing the aggregate number of shares of common stock offered by some of the selling stockholders by 50,000 shares and increasing by 7,500 the shares subject to purchase upon exercise of the underwriters' option to purchase additional shares of common stock from the Registrant. Pursuant to Rule 462(b), the contents of the Registration Statement on Form S-1, as amended (File No. 333-133032), including the exhibits and the power of attorney thereto, are incorporated by reference into this Registration Statement.


PART II
INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 16. Exhibits and Financial Statement Schedules.

(a)
The following exhibits are filed herewith:

Number
   Exhibit Title
5.01   Opinion of Fenwick & West LLP regarding legality of the securities being registered.

23.01
 
Consent of Fenwick & West LLP (included in Exhibit 5.01).

23.02
 
Consent of Independent Registered Public Accounting Firm.

24.01
 
Power of Attorney (filed as Exhibit 24.01 to the Registrant's Registration Statement on Form S-1 (File No. 333-133032) filed on April 6, 2006, and incorporated herein by reference).


SIGNATURES

        Pursuant to the requirements of the Securities Act, the Registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of San Diego, State of California, on this 26th day of April, 2006.

    DEXCOM, INC.

 
 
By:
 
/s/  ANDREW P. RASDAL      
Andrew P. Rasdal
 President and Chief Executive Officer

        Pursuant to the requirements of the Securities Act, this Registration Statement has been signed by the following persons in the capacities and on the date indicated.

Name
   Title
   Date

 
 
 
 
 

Principal Executive Officer:
 
 
 
 

/s/  ANDREW P. RASDAL      
Andrew P. Rasdal
 
President, Chief Executive Officer and Director
 
April 26, 2006

Principal Financial Officer and Principal
Accounting Officer:
 
 

/s/  STEVEN J. KEMPER      
Steven J. Kemper
 
Chief Financial Officer
 
April 26, 2006

Additional Directors:
 
 
 
 

*
Donald L. Lucas
 
Chairman of the Board of Directors
 
April 26, 2006

*
Brent Ahrens
 
Director
 
April 26, 2006

*
Kim D. Blickenstaff
 
Director
 
April 26, 2006

*
Sean Carney
 
Director
 
April 26, 2006

*
Terrance H. Gregg
 
Director
 
April 26, 2006

*
Donald A. Lucas
 
Director
 
April 26, 2006
         


*
Glen D. Nelson, M.D.
 
Director
 
April 26, 2006

*
Jay S. Skyler, M.D.
 
Director
 
April 26, 2006
*By: /s/  STEVEN J. KEMPER      
Steven J. Kemper
Attorney-in-Fact		        


EXHIBIT INDEX

Number
   Exhibit Title
5.01   Opinion of Fenwick & West LLP regarding legality of the securities being registered.

23.01
 
Consent of Fenwick & West LLP (included in Exhibit 5.01).

23.02
 
Consent of Independent Registered Public Accounting Firm.

24.01
 
Power of Attorney (filed as Exhibit 24.01 to the Registrant's Registration Statement on Form S-1 (File No. 333-133032) filed on April 6, 2006, and incorporated herein by reference).



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EXPLANATORY NOTE AND INCORPORATION OF CERTAIN INFORMATION BY REFERENCE
PART II INFORMATION NOT REQUIRED IN PROSPECTUS
SIGNATURES
EXHIBIT INDEX