Ronald Williams will be retiring from the post of chief executive officer (CEO) of Aetna Inc. Nov. 29, the company says.

Mark Bertolini, 54, will take over fromWilliams, 60, as CEO that day, according to Aetna, Hartford (NYSE:AET).

Bertolini, who is now president and head of business operations at Aetna, will be elected to the company’s board around that time, the company says.

Williams will serve as an executive chairman for several months, and then retire in April 2011. The Aetna board intends to make Bertolini chairman when Williams retires, the company says.

Williams has agreed to serve as a consultant to Aetna until February 2012, the company says.

“After nearly 10 years at Aetna and with the company performing well, it is time to step aside,” Williams says in a statement about his upcoming departure. “The passage of major health care reform legislation has underscored the need for market-based solutions to address quality and affordability challenges in health care, and the next few years will present another opportunity for Aetna to lead.”

Bertolini, a long-time health insurance industry veteran, began working for Aetna in February 2003. He has been president of the company since July 2007.

- Allison Bell

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CORRECTION: An earlier version of this article described Ronald Williams’ retirement plans incorrectly. Williams plans to retire first from the CEO post and later to retire from his position as Aetna’s chairman.