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 *
  BAKER BROS ADVISORS LLC
 2. Date of Event Requiring Statement (Month/Day/Year)
04/12/2012		 3. Issuer Name and Ticker or Trading Symbol
SEATTLE GENETICS INC /WA [SGEN]
(Last)
(First)
(Middle)
667 MADISON AVENUE 21ST FLOOR		 4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

NEW YORK, NY US 10065		 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 0
I (1) (2) (3) (4)
See footnote (1) (2) (3) (4)

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

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
BAKER BROS ADVISORS LLC
667 MADISON AVENUE 21ST FLOOR
NEW YORK, NY US 10065		   X   X    

Signatures

BAKER BROS. ADVISORS, LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 04/23/2012
**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) Baker Bros. Advisors, LLC ("the Adviser") serves as the Investment Adviser to Baker Brothers Life Sciences, L.P. (direct holder of 15,131,223 shares), 14159, L.P. (direct holder of 323,148 shares), 667, L.P. (direct holder of 4,966,001 shares), Baker Bros. Investments II, L.P. (direct holder of 272,635 shares), Baker Bros. Investments, L.P. (direct holder of 266,495 shares), and Baker Tisch Investments, L.P. (direct holder of 450,461 shares)("the Funds"). In connection with the services provided by the Adviser, the Adviser receives an asset based management fee that does not confer any pecuniary interest.
(2) On April 12, 2012, the Adviser, the Funds, and the general partners of the Funds entered into an amended and restated management agreement which gave the Adviser complete and unlimited discretion and authority with respect to the Funds' investments and voting power over investments. The general partners of the Funds relinquished all discretion and authority with respect to the Funds' investments and voting power over investments.
(3) Julian C. Baker and Felix J. Baker each may be deemed to control the Adviser and to indirectly beneficially own the shares beneficially owned by it. Julian C. Baker and Felix J. Baker disclaim beneficial ownership of these securities, except to the extent of their pecuniary interest therein and this report shall not be deemed an admission that Felix J. Baker or Julian C. Baker is the beneficial owner of the above referenced securities for purposes of Section 16 or for any other purpose.
(4) The shares over which the Adviser is reporting have already been reported by Felix J. Baker and Julian C. Baker in their own Forms 3 and 4. In the future, the Adviser may jointly file Section 16 reports with Julian C. Baker and Felix J. Baker. Felix Baker is a Director of the Issuer.
 
Remarks:
For purposes of Section 16 of the Securities and Exchange Act of 1934, as amended (the "Exchange Act"), Baker Bros. Advisors, LLC is a director by deputization by virtue of its representation on the Board of Directors of Seattle Genetics, Inc.  The filing of this statement shall not be deemed an admission that the reporting person is the beneficial owner of any securities not held directly for its account for purposes of Section 16 of the Exchange Act, or otherwise.

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