Privately-held Nielsen said it would pay about $327 million to buy the 40% stake in NetRatingsthat it does not already own.
Nielsen said it would pay $21.00 a share in cash for the remaining stake of the Internet media and market research company. The price represents a 16% premium to NetRatings' closing price on Friday, and also is substantially higher than an earlier offer by Nielsen.
In October, Nielsen proposed to buy the minority stake for $16 per share in cash. The new price represents about a 44% premium over NetRatings' closing stock price prior to that offer.
Shares of NetRatings surged after the deal was announced.
The takeover is expected to close in the second quarter.
"This transaction will provide fair value to NetRatings shareholders while also allowing Nielsen and NetRatings to better coordinate their strengths for the benefit of our mutual clients," Nielsen Chief Executive David Calhoun said in a statement.
Nielsen, known as the dominant television ratings agency in the United States, recently changed its name from VNU after going private in a leveraged buyout last year.
The private equity groups that bought VNU include Carlyle Group and Kohlberg Kravis Roberts & Co. They pledged to keep the company substantially together as an integrated company for the first 18 months after the buyout.