Carly Fiorina's sudden departure from HP is part of a trend of increased turnover among U.S. CEO's.

NEW YORK (CNN/Money) - Wednesday's sudden departure of Hewlett Packard CEO Carly Fiorina is just the most public example of a growing trend in turnover at the top of America's corporate ladders.

Outplacement firm Challenger, Gray and Christmas said its survey of CEO turnover found that January had 92 CEO's leaving their jobs, the greatest number of departures in any month since February 2001. That's almost double the 50 CEOs who found the door in January 2004 and up from the 56 who left the top job in December.

The reason most often stated for a departure in January was retirement, the reason given for 35 of the departures, although the average age of those who "retired" was only 61, according to the Challenger survey. Another 21 found different positions within the company while 14 were simply listed as resignations.

Fiorina, the CEO of HP since 1999, left HP (Research) Wednesday due to differences with the company's board of directors. She had been the engineer of the 2003 acquisition of Compaq that some blamed for problems with the company's performance.

"Like many post-merger CEOs find, it is a real struggle to put together two completely different corporate cultures, a fact which undoubtedly contributed to Fiorina's demise," said John Challenger, CEO of the search firm.

But Challenger said even companies not involved in mergers are putting more pressure to perform on their CEOs.

"Today's CEO is under fire from a number of sectors," said Challenger. "Not only are shareholders demanding higher and higher returns, directors are far more active and government agencies are increasingly putting them under the microscope."

Challenger said that risk of turnover is the reason that a survey last year by Burson-Marsteller found that 60 percent of executives did not want the CEO job, up from only 27 percent who didn't want the job in 2001.

"All this scrutiny is taking the fun out of being CEO," he said. "The pay may be high and the perks plentiful but the likelihood of being publicly ousted within three or four years by angry shareholders may not be worth the riches."