For all their accomplishments, a quick study of precedent suggests that the C.F.O. job has effectively been a glass ceiling for women in finance. Despite its vaunted status in the corporate hierarchy, C.F.O. is rarely a path to the C.E.O. suite for anyone. (Stan O'Neal, the recently ousted Merrill Lynch chief executive, was an exception, but he is now seen as a disastrous example of what happens when a "numbers guy" gets to run the whole show.) According to CFO magazine, the number of Fortune 500 companies with female C.F.O.'s last year was 38, or 7.6 percent, whereas in 1995, there were 10, or 2 percent. The pace of advancement can be described only as slow, but the C.F.O.'s office looks downright progressive compared with that of the C.E.O.  Of the Fortune 500 companies, only 12, or 2.4 percent, have female chief executives (with zero on Wall Street), though that is certainly up from 1996, when there were none.

In banking and finance, the C.F.O. position is perceived as more of a support role—albeit a critical one—in which one keeps the books and deals with balance sheets and regulators, providing guidance to the C.E.O.  (To some, the job fits into the age-old gender stereotype of women as keepers of the family checkbook.) Meanwhile, the traders and bankers go out hunting, risking the firm's capital and bringing in the revenues (or losses) that drive the business; they are the cowboys who ultimately fill the pool of future chief executives. Of the current C.E.O.'s at the top seven Wall Street investment banks, six served previously as chief operating officers, responsible for day-to-day activities rather than toiling behind the scenes. Often, the top dog's background reflects a particular bank's culture and priorities: At firms that live and die by trading profits, for example, the chief tends to rise through the trading arm (as was the case with Goldman Sachs head Lloyd Blankfein and Fuld, Lehman's chief).

Ironically, when Callan's C.F.O. opportunity came along, she held just the sort of swashbuckling job that could have groomed her for future C.E.O. consideration. As head of Lehman's hedge fund investment-banking unit, she was knee-deep in leading I.P.O.'s for companies like Fortress, Blackstone, and Och-Ziff Capital Management Group. She was also instrumental in initiating a $500 million bond issue by Citadel Investment Group in 2006, the first such bond offering by a hedge fund. When she was approached about the C.F.O. position, she hesitated—but only for a second.

"My first reaction was 'Is it even conceivable that I wouldn't do it?' And I knew the answer was no," she says. "I had a desire that was building to be more of an opinionmaker, to have more influence in the organization."

On a late-autumn evening shortly after her promotion, Callan darts periodically across her office to check on the pricing of the Och-Ziff I.P.O.  A video screen pipes in images of her old trading desk. Framed photographs of her dogs are spread liberally across the shelves and wall where some executives might display portraits of their wife and kids.

"I did not have a single female client at any level of these organizations," she says of the hedge fund world she used to deal with. "This was a 100 percent male-dominated industry." She adds, however, that she managed to turn her outsider status into an advantage, one that helped her build trust as she served as an adviser and hand-holder to rich hedge fund founders with scary reputations—men like Citadel's Griffin and Cohen of SAC Capital Advisors. "I think people may let their guard down more with me than with others. Being different—being a woman—was helpful," she says.

Dwarfed by the high-backed leather chair in her office, Callan is wearing a short crocheted dress with a black belt slung low around her hips, gold hoop earrings, and knee-high caramel-colored high-heel boots. She seems to have rejected the path taken by some of her counterparts, who have erased all signs of their femininity to blend in with the pinstripes. "I don't subordinate my feminine side," she says. "I'm very open about it. I have no problem talking about my shopper or my outfit."