As filed with the Securities and Exchange Commission on May 16, 2013

Registration No. 333-     

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

STEMLINE THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

750 Lexington Avenue
Sixth Floor
New York, New York 10022
(646)502-2310
(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Ivan Bergstein, M.D.
Chairman, President and Chief Executive Officer
Stemline Therapeutics, Inc.
750 Lexington Avenue
Sixth Floor
New York, New York 10022
(646)502-2310
(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

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

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.  x Registration No. 333-188378

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

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

CALCULATION OF REGISTRATION FEE

This registration statement shall become effective upon filing with the Securities and Exchange Commission in accordance with Rule 462(b) under the Securities Act, as amended.

EXPLANATORY NOTE AND INCORPORATION BY REFERENCE

This registration statement is being filed pursuant to Rule 462(b) under the Securities Act of 1933, as amended, for the purpose of registering additional shares of common stock, par value $0.0001 per share, of Stemline Therapeutics, Inc., a Delaware corporation. The contents of the Registrant’s earlier Registration Statement on Form S-1 (File No. 333-188378), as amended, which was declared effective on May 16, 2013, are incorporated herein by reference into, and shall be deemed part of, this registration statement.

The required opinions and consents are listed on an Exhibit Index attached hereto and filed herewith.

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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 New York, State of New York, on this 16th day of May, 2013.

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

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EXHIBIT INDEX

* Previously filed as part of the Registrant’s Registration Statement on Form S-1 (File No. 333-188378) filed with the Commission on May 6, 2013.

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