Women comprised only 8.8 percent of active physicians in the United States in 1977. However, recent trends in the sex composition of medical school classes indicate that women will make up at least one-fourth of total physician supply in the future. Consequently, the effect of sex-composition changes on the supply of physicians' services is of importance, especially since much current federal policy is based upon assumptions about physician behavior drawn from observation of the current stock of physicians. This article explores the issue of differences by sex in lifetime earnings associated with alternative specialty choices. Economic incentives to specialize rather than enter general/family practice are examined initially. Then the incentives influencing the decision to specialize in either primary care or non-primary care fields are considered. Findings are reviewed and implications for future trends in specialty distribution of physicians, as well as implications for current and future federal policy affecting physicians' specialty decisions, are discussed.