Objective: To examine the current supply and distribution of obstetrician-gynecologists and project future supply under various scenarios. Methods: A discrete actuarial supply model was developed, and practice patterns were analyzed. Supply projections under different scenarios, distributions, and practice profiles were examined. Results: Women are expected to become the majority of practitioners by 2014. Continuation of current residency output will result in slow to no growth in obstetrician-gynecologist–to-female population ratios over the next 20 years. A minor (10%) reduction in specialty training would slow specialty growth over the next decade, followed by a slight reduction in supply. Services provided chiefly involve ambulatory reproductive health care, pregnancy, and surgical correction of conditions specific to the female genitourinary system. Even though the proportion of deliveries performed by midwives has increased and family practitioners have maintained their share, obstetrician-gynecologists provide the vast majority of obstetric care and virtually all services for perinatal complications. Generalist services represent relatively minor aspects of their practices. Care of the aged female population is highly fragmented among specialties; more than 50% of all aged Medicare beneficiaries who saw an obstetrician-gynecologist at least once failed to receive a majority of services from any one physician specialty. Conclusion: On the basis of trends in patient demographics and care patterns, obstetrician-gynecologists must resolve whether to provide more generalist office-based care, especially to the rapidly growing older female population, or to invest more intensively in surgical specialty care. The specialty’s unique contributions to women’s health should influence this decision.