Aetna said it would continue its Medicare H.M.O. operations in New York City, but would leave Nassau, Suffolk, Orange, Putnam and Dutchess Counties in New York.
But the company said that it has been successfully audited for its Medicare billing practices, and that it is "confident it will prevail and ultimately be exonerated".
The federal government could have companies release their price sheets, and the government could make public all the data it already collects from its Medicare and Medicaid purchases.
Robert J. Dondes, president of Health Central, said his company had decided to pull out because of the losses it would sustain on its Medicare business.
For now, UnitedHealth seems intent on doubling down on its Medicare Advantage bet, saying it plans to focus on recruiting new members in Boston, Washington, Atlanta and Chicago.
HCA has put its Medicare fraud woes behind it and looks strong financially.
Genworth Financial said Monday it has agreed to sell its Medicare supplement business to Aetna for $290 million.
Aetna said it was "reviewing future options for its Medicare business on a market-by-market basis and expects to exit a number of markets next year".
The company nabbed $300 million and announced that it would begin enrolling members to its Medicare Advantage plan in eight Florida counties.
The company also told analysts during a conference call that it added more than 120,000 customers to its Medicare Advantage program this month.
Tenet said that its Medicare payments had been appropriate and that it would provide more information shortly.
