Behind the physician licensure numbers: false impressions, retirement crisis, and migration.

This communication examines the supply of primary-care physicians at the state level. It shows that the number of actively practicing physicians is considerably less than the number of licensed physicians; the age distribution of primary-care physicians has a bulge in the ages younger than 50, and this bulge may lead in the near future to an unexpected increase in physician attrition due to retirement; and, at the state level, migration may be playing the dominant role in determining the total supply of primary-care physicians.