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 FELIX 2. Date of Event Requiring Statement (Month/Day/Year) 06/22/2015 3. Issuer Name and Ticker or Trading Symbol ALEXION PHARMACEUTICALS INC [ALXN] (Last) (First) (Middle) 667 MADISON AVENUE, 21ST FLOOR 4. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) 5. If Amendment, Date Original Filed(Month/Day/Year) (Street) NEW YORK, NY 10065 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ 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)

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 FELIX 667 MADISON AVENUE, 21ST FLOOR NEW YORK, NY 10065	  X	Â	Â	Â
BAKER JULIAN 667 MADISON AVENUE, 21ST FLOOR NEW YORK, NY 10065	  X	Â	Â	Â
BAKER BROS. ADVISORS LP 667 MADISON AVENUE, 21ST FLOOR NEW YORK, NY 10065	  X	Â	Â	Â
Baker Bros. Advisors (GP) LLC 667 MADISION AVENUE 21ST FLOOR NEW YORK, NY 10065	  X	Â	Â	Â
667, L.P. 667 MADISON AVENUE 21ST FLOOR NEW YORK, NY 10065	  X	Â	Â	Â
Baker Brothers Life Sciences LP 667 MADISON AVENUE, 21ST FLOOR NEW YORK, NY 10065	  X	Â	Â	Â

Signatures

/s/ Felix J. Baker		06/24/2015
**Signature of Reporting Person		Date
/s/ Julian C. Baker		06/24/2015
**Signature of Reporting Person		Date
Baker Bros. Advisors LP Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing		06/24/2015
**Signature of Reporting Person		Date
Baker Bros. Advisors (GP) LLC, Name:Scott L. Lessing, Title: President /s/ Scott L. Lessing		06/24/2015
**Signature of Reporting Person		Date
Baker Bros. Advisors LP, Mgmt. Co. and Inv. Adviser to 667, L.P., pursuant to authority granted by Baker Biotech Capital, L.P., GP to 667, L.P. Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing		06/24/2015
**Signature of Reporting Person		Date
Baker Bros. Advisors LP, Mgmt. Co. and Inv. Adviser to Baker Brothers Life Sciences, L.P., pursuant to authority granted by Baker Brothers Life Sciences Capital, L.P., GP to Baker Brothers Life Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing		06/24/2015
**Signature of Reporting Person		Date

Explanation of Responses:

No securities are beneficially owned
*	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).
  Remarks: Felix J. Baker is a director of Alexion Pharmaceuticals, Inc. (the "Issuer"). For purposes of Section 16 of the Securities Exchange Act of 1934, as amended the Reporting Persons other than Felix J. Baker are deemed directors by deputization by virtue of their representation on the Board of the Issuer.

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

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