UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-Q/A

Amendment No. 1

For the quarterly period ended June 30, 2012

OR

For the transition period from              to             

Commission File Number 001-31574

AMERIGROUP Corporation

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code:

(757) 490-6900

N/A

(Former name, former address and former fiscal year, if changed since last report)

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  x    No  ¨

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):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ¨    No  x

As of July 30, 2012, there were 48,628,340 shares outstanding of the Company’s common stock, par value $0.01 per share.

EXPLANATORY NOTE

AMERIGROUP Corporation is filing this amendment (the “Form 10-Q/A”) to its Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2012 (the “Form 10-Q”) filed with the U.S. Securities and Exchange Commission (“SEC”) on August 3, 2012, solely to re-file Exhibit 32 to correct the period reference in such Exhibit.

This Form 10-Q/A speaks as of the date of the Form 10-Q and no attempt has been made to modify or update disclosures in the original Form 10-Q except as noted above. This Form 10-Q/A does not reflect events occurring after the filing of the Form 10-Q or modify or update any related disclosures. Information not affected by this Form 10-Q/A is unchanged and reflects the disclosure made at the time of the filing of the Form 10-Q with the SEC. Accordingly, this 10-Q/A should be read in conjunction with the original Form 10-Q.

The Exhibit Index identified under Part II, Item 6. of the Form 10-Q is hereby amended such that the following documents are (i) amended and added to the Exhibit Index and (ii) included as exhibits to the Form 10-Q:

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this Report to be signed on its behalf by the undersigned thereunto duly authorized.