These days, the CFO job at a financial-services firm is the perfect gig for a short-timer.

Unlike at big tech companies -- where a chief financial officer often can hang on for years just balancing the books and exercising stock options -- the lifespan of a CFO on Wall Street increasingly seems to be measured in months.

In December, Al de Molina resigned as Bank of America's ( BAC) CFO, just 18 months after getting the job. On Monday, investors learned that Sallie Krawcheck's tenure as Citigroup's ( C) top financing officer won't be much longer than Molina's.

Krawcheck, who is moving back to run Citigroup's brokerage, private banking and stock research operations, became CFO just over two years ago, in September 2004.

In her quick turnaround, Krawcheck is hardly alone. Jerome Bailey, who left insurance broker Marsh & McClennan ( MMC) early last year to become the CFO of the New York Mercantile Exchange ( NMX), lasted just seven months at Nymex. The exchange pushed Bailey out the door on the eve of its highly successful IPO last November.

In many ways, the CFO position on Wall Street is a thankless job with little glamour -- even if it is certainly well-compensated. For many, it's either a stepping stone to a better job, or a temporary stint.

The job of the CFO at all companies has become increasingly more stressful with the stiffened reporting mandates under the Sarbanes/Oxley corporate governance reform law. But bank CFOs have had the added pressure of dealing with a tricky interest rate environment, which makes it hard for lenders to find high-yielding investment opportunities to reinvest customer deposits.

Someone taking the CFO job at a financial firm often has his or her eye on becoming the CEO down the road or on another top job within the company. And when that doesn't happen, it often is time to hit the road.

Indeed, when Citigroup CEO Chuck Prince promoted Krawcheck, most saw it as way of grooming the former hot-shot stock analyst for a bigger and better post at Citigroup. But in the past year, she has become the main lightning rod for criticism of Citigroup's middling financial performance.

People familiar with Citigroup say Krawcheck is still thought well of within the bank. But the heat she drew as CFO may have dimmed her star -- at least for the moment. Some say they wouldn't be surprised if Krawcheck eventually packed her bags.

"In other companies, being a CFO is an end to itself," says Tim Ghriskey, chief investment officer for Solaris Asset Management. "But at a financial company, it's often a grooming position. The perception is it's a bit of a revolving door."

When de Molina stepped down from BofA, he was quoted by Bloomberg as saying that the job of CFO was a "little less fun." Bank officials also said the former CFO had expressed an interest in running his own company.

Of course, it wasn't always that way. Dina Dublon, once one of the highest-ranking female executives on Wall Street, served as JPMorgan Chase's ( JPM) CFO for six years before retiring in 2004.

Today, for a bank CFO, that's almost an eternity.

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