NEW YORK — Waterfront Media, operator of the Everyday Health Network Web sites, said yesterday it would buy the Revolution Health Network, founded by America Online founder and former Hawai'i resident Steve Case.

The combination will create a company that will rival WebMD Health Corp. in Web traffic.

The companies did not disclose terms of the agreement, which they expect to close by mid-October. Waterfront said it is the largest privately held online health company, and the combined company will keep the Waterfront name.

Sites in the Everyday Health network include EverydayHealth.com along with WhatToExpect.com, SouthBeachDiet.com and Jillian Michaels.com. Revolution's network includes RevolutionHealth .com, HealthTalk .com and Care Pages.com.

Case is Revolution's chairman and chief executive, and he will join Waterfront's board of directors. Waterfront founder and Chief Executive Ben Wolin will be CEO of the combined company.

Stifel Nicolaus & Co. analyst George Askew said the companies are growing faster than WebMD Health, and their combination will help bring more health-related ads online and lead to more consolidation in the sector. He said Revolution and Waterfront currently have a total of 304 million combined page views and 22.5 million unique users per month.