As filed with the Securities and Exchange Commission on October 2, 2013

Registration No. 333-[    ]

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

MEDASSETS, INC.

(Exact name of registrant as specified in its charter)

100 North Point Center East, Suite 200

Alpharetta, Georgia 30022

(678) 323-2500

(Address, including zip code of Principal Executive Offices)

Long Term Performance Incentive Plan

(Full title of the plan)

Jonathan H. Glenn, Esq.

Executive Vice President, Chief Legal Officer and Corporate Secretary

MedAssets, Inc.

100 North Point Center East, Suite 200

Alpharetta, Georgia 30022

(678) 323-2500

(Name, Address, including Zip Code, and Telephone Number, including Area Code, of agent for service)

Copies to:

Steven J. Gartner, Esq.

Morgan D. Elwyn, Esq.

Willkie Farr & Gallagher LLP

787 Seventh Avenue

New York, New York 10019

(212) 728-8000

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. (Check one):

CALCULATION OF REGISTRATION FEE

-2-

EXPLANATORY NOTE

This registration statement on Form S-8 (this “Registration Statement”) is filed by MedAssets, Inc. (the “Company”), to register an additional 2,600,000 shares of the Company’s Common Stock, par value $0.01 per share (the “Common Stock”), issuable pursuant to the Long Term Performance Incentive Plan, as amended (the “Plan”). Pursuant to the Registration Statement on Form S-8 (File No. 333-156505) filed by the Company on December 30, 2008 (the “Prior Registration Statement”), the Company previously registered an aggregate of 13,781,463 shares of Common Stock issuable pursuant to the Plan. On April 25, 2013, the Company’s Board of Directors approved an amendment to the Plan to increase the number of shares issuable thereunder by 2,600,000 shares of Common Stock, which was approved by the Company’s stockholders at the Company’s annual meeting on June 13, 2013. This Registration Statement relates to the additional 2,600,000 shares of Common Stock issuable pursuant to the Plan. This Registration Statement relates to securities of the same class as that to which the Prior Registration Statement relates and is submitted in accordance with General Instruction E to Form S-8 regarding registration of additional securities. Pursuant to General Instruction E of Form S-8, the contents of the Prior Registration Statement is incorporated herein by reference and made a part hereof, except as otherwise updated or modified by this Registration Statement.

PART II

INFORMATION REQUIRED IN THE

REGISTRATION STATEMENT

The Prior Registration Statement and the following documents, filed with the United States Securities and Exchange Commission (the “Commission”) by the Company, are incorporated by reference into the Registration Statement:

In addition, all documents filed by the Company with the Commission pursuant to Sections 13(a), 13(c), 14, and 15(d) of the Exchange Act subsequent to the date of this Registration Statement and prior to the filing of a post-effective amendment to this Registration Statement which indicates that all the securities offered hereby have been sold or which deregisters all securities then remaining unsold shall be deemed to be incorporated by reference in this Registration Statement and to be a part hereof from the date of the filing of such documents with the Commission. Any statement contained in a document incorporated by reference herein shall be deemed to be modified or superseded for purposes hereof to the extent that a statement contained herein (or in any other subsequently filed document which also is incorporated by reference herein) modifies or supersedes such statement. Any statement so modified or superseded shall not be deemed to constitute a part hereof except as so modified or superseded. Nothing in this Registration Statement shall be deemed to incorporate by reference any documents or portions thereof, whether specifically listed above or filed in the future, that are not deemed “filed” with the SEC pursuant to applicable securities laws and regulations unless the Company expressly provides to the contrary that such documents or portions thereof is incorporated by reference herein.

The Exhibits to this Registration Statement are listed in the Exhibit Index and incorporated herein by reference.

SIGNATURES

Pursuant to the requirements of the Securities Act, the Company certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Alpharetta, State of Georgia, on the 2nd day of October 2013.

POWER OF ATTORNEY

Each person whose signature appears below constitutes and appoints John A. Bardis and Jonathan H. Glenn as his or her true and lawful attorney-in-fact and agent, each acting alone with full power of substitution and resubstitution, for him or her and in his or her name, place, and stead, in any and all capacities, to sign any or all amendments (including post-effective amendments) and exhibits to this Registration Statement, and to any registration statement filed under Commission Rule 462, and to file the same, with all exhibits thereto, and all documents in connection therewith, with the Commission, granting unto said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorney-in-fact and agent, or his or her substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

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

INDEX TO EXHIBITS