EX-5.1

Exhibit 5.1

ROPES & GRAY LLP

PRUDENTIAL TOWER

800 BOYLSTON STREET

BOSTON, MA 02199-3600

WWW.ROPESGRAY.COM

March 7, 2019

Sarepta Therapeutics, Inc.

215 First Street

Suite 415

Cambridge, Massachusetts 02142

Re: Registration Statement on Form S-3 (Registration No. 333-229934)

Ladies and Gentlemen:

We have acted as counsel to Sarepta Therapeutics, Inc., a Delaware corporation (the “Company”) in connection with issuance and sale of up to 2,994,792 shares of the common stock, $0.0001 par value (the “Shares”), of the Company pursuant to the above-referenced registration statement (as amended through the date hereof, the “Registration Statement”), filed by the Company with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933 (the “Securities Act”). The Shares are being sold pursuant to an underwriting agreement, dated March 5, 2019 (the “Underwriting Agreement”), among the Company and the representatives of the underwriters named therein.

In connection with this opinion letter, we have examined such certificates, documents and records and have made such investigation of fact and such examination of law as we have deemed appropriate in order to enable us to render the opinions set forth herein. In conducting such investigation, we have relied, without independent verification, upon certificates of officers of the Company, public officials and other appropriate persons.

The opinions expressed below are limited to the Delaware General Corporation Law.

Based upon and subject to the foregoing, we are of the opinion that the Shares have been duly authorized and, when issued and delivered pursuant to the Underwriting Agreement against payment of the consideration set forth therein, will be validly issued, fully paid and non-assessable.