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As filed with the Securities and Exchange Commission on December 14, 2006

Registration No. 333-            



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


FORM S-1
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933


AFFYMAX, INC.
(Exact name of registrant as specified in its charter)


Delaware   2834   77-0579396
(State or other jurisdiction of
incorporation or organization)
  (Primary Standard Industrial
Classification Code Number)
  (I.R.S. Employer
Identification Number)

4001 Miranda Avenue
Palo Alto, CA 94304
(650) 812-8700

(Address, including zip code, and telephone number, including
area code, of registrant's principal executive offices)


Arlene M. Morris
President and Chief Executive Officer
4001 Miranda Avenue
Palo Alto, CA 94304
(650) 812-8700
(Name, address, including zip code, and telephone number, including area code, of agent for service)


Copies to:
Laura A. Berezin, Esq.
Barbara A. Kosacz, Esq.
Cooley Godward Kronish LLP
Five Palo Alto Square
3000 El Camino Real
Palo Alto, CA 94306-2155
(650) 843-5000
  Bruce K. Dallas, Esq.
Davis Polk & Wardwell
1600 El Camino Real
Menlo Park, CA 94025
(650) 752-2000

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, 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 333-136125

        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 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 $.001 per share   230,000(1)   $25.00   $5,750,000.00   $615.25

(1)
Includes 30,000 shares subject to the underwriters' over-allotment option.





Explanatory Note

        This registration statement relates to the Registration Statement on Form S-1, Securities and Exchange Commission File No. 333-136125 (the "Prior Registration Statement") and is filed pursuant to Rule 462(b) promulgated under the Securities Act of 1933, as amended, and Instruction V to Form S-1, solely to increase the number of shares of the Registrant's common stock registered under the Prior Registration Statement by 230,000 shares. The contents of the Prior Registration Statement are hereby incorporated by reference.


CERTIFICATION

        The Registrant hereby certifies to the Commission that (i) it has instructed its bank to pay the Commission the filing fee set forth on the cover page of this Registration Statement by a wire transfer of such amount to the Commission's account at Mellon Bank as soon as practicable (but no later than the close of business on December 15, 2006), (ii) it will not revoke such instructions, (iii) it has sufficient funds in the relevant account to cover the amount of such filing fee, and (iv) it will confirm receipt of such instructions by its bank during the bank's regular business hours no later than December 15, 2006.



SIGNATURES

        Pursuant to the requirements of the Securities Act of 1933, the Registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Palo Alto, State of California, on the 14th day of December, 2006.

    AFFYMAX, INC.

 

 

By:

 

/s/  
PAUL B. CLEVELAND      
Paul B. Cleveland
Executive Vice President, Corporate Development and Chief Financial Officer

        Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated.

Signature

  Title

  Date

/s/  ARLENE M. MORRIS*      
Arlene M. Morris

 

President, Chief Executive Officer and Member of the Board of Directors (
Principal Executive Officer)

 

December 14, 2006

/s/  PAUL B. CLEVELAND*      
Paul B. Cleveland

 

Executive Vice President, Corporate Development and Chief Financial Officer
(Principal Financial Officer)

 

December 14, 2006

/s/  ALI MAHDAVI*      
Ali Mahdavi

 

Vice President, Finance and Administration
(
Principal Accounting Officer)

 

December 14, 2006

/s/  JOHN P. WALKER*      
John P. Walker

 

Member of the Board of Directors

 

December 14, 2006

/s/  NICHOLAS G. GALAKATOS, PH.D.*      
Nicholas G. Galakatos, Ph.D.

 

Member of the Board of Directors

 

December 14, 2006

/s/  KATHLEEN LAPORTE*      
Kathleen LaPorte

 

Member of the Board of Directors

 

December 14, 2006

/s/  ELIZABETH CZEREPAK*      
Elizabeth Czerepak

 

Member of the Board of Directors

 

December 14, 2006

/s/  HIRONORI HOZOJI*      
Hironori Hozoji

 

Member of the Board of Directors

 

December 14, 2006

/s/  R. LEE DOUGLAS*      
R. Lee Douglas

 

Member of the Board of Directors

 

December 14, 2006
         


/s/  TED W. LOVE*      
Ted W. Love

 

Member of the Board of Directors

 

December 14, 2006

/s/  DANIEL K. SPIEGELMAN*      
Daniel K. Spiegelman

 

Member of the Board of Directors

 

December 14, 2006

*By:

 

/s/  
PAUL B. CLEVELAND      
Paul B. Cleveland
Attorney-in-fact

 

 


EXHIBIT INDEX

Exhibit
Number

  Description of Document

5.1   Opinion of Cooley Godward Kronish LLP
23.1   Consent of independent registered public accounting firm
23.2 Consent of Cooley Godward Kronish LLP. Reference is made to Exhibit 5.1
24.1 Power of Attorney
Incorporated by reference from Exhibit 24.1 to the Registration Statement on Form S-1 of the Registrant, File No. 333-136125.



QuickLinks

CALCULATION OF REGISTRATION FEE
Explanatory Note
CERTIFICATION
SIGNATURES
EXHIBIT INDEX