Good question asked by The New York Times:
"HUNDREDS of feet above Manhattan, the reception area of Proskauer Rose’s headquarters boasts all of the muscular, streamlined ornamentation that symbolizes authority and power in a big city law firm — modern art, contemporary furniture, white marble floors, high ceilings and stunning views. The background music floating about this particular stage set is composed of the steady, reassuring cadences of talented, ambitious lawyers greeting their clients.
[snip]
"Although the nation’s law schools for years have been graduating classes that are almost evenly split between men and women, and although firms are absorbing new associates in numbers that largely reflect that balance, something unusual happens to most women after they begin to climb into the upper tiers of law firms. They disappear.
"According to the National Association for Law Placement, a trade group that provides career counseling to lawyers and law students, only about 17 percent of the partners at major law firms nationwide were women in 2005, a figure that has risen only slightly since 1995, when about 13 percent of partners were women.
"Even those who have made it to the top of their profession say that the data shows that women’s legal careers [PDF link] involve distinct, often insurmountable hurdles and that those hurdles remain misunderstood or underexamined."
There’s much more info in this interesting article!