WellPoint says it will pay $92 for each Amerigroup share. That's a 43 percent premium to the company's closing price Friday of $64.34.
Amerigroup currently has about 48.5 million outstanding shares, according to FactSet.
The companies put the total value of the deal at approximately $4.9 billion.
WellPoint is based in Indianapolis, while Amerigroup is based in Virginia Beach, Va.
The transaction is expected to close in 2013's first quarter. It still needs certain regulatory approvals and the approval of Amerigroup stockholders.
The deal is expected to add to WellPoint's 2013 earnings per share and add more than $1 per share by 2015.