This study analyzes how the growing proportion of women in the United States physician population will affect the amount and type of physician services available to the US population. Female physicians work fewer hours per week, are slightly less likely to be in patient care, and tend to enter different specialties than male physicians. Female physicians also have higher retirement rates than male physicians, but due to their lower mortality rates, have work lives nearly as long as male physicians. We examined how the changing composition of the physician population will affect the availability of physician services by comparing historical and projected trends for the number of active post-residency physicians with comparable trends for a full-time-equivalent measure of physician supply. The full-time-equivalent measure takes into account the different labor supply behavior of key subpopulations (e.g., women and graduates of US versus foreign medical schools). The results suggest that the changing composition of the physician population will reduce the growth of effective physician supply between 1986 and 2010 but only by four percentage points.