The number of physicians practicing in the nonmetropolitan areas of the United States in relation to population has increased over the past two decades, but more slowly than the number of physicians in metropolitan counties. During the same period, there was a growing acceptance of the perception that the physician work force in the United States exceeded the number necessary to meet the requirements of an efficient health care system. This has caused policy-makers to consider reforming the incentives for training physicians and restricting the entry of physicians from other countries into the United States. The supply figures on which these assessments of oversupply were made are based on "head counts" of the number of licensed, active physicians. By using more detailed data describing the licensed practicing physicians in the states of North Carolina and Washington, and by using estimates of professional activity collected as part of the Socioeconomic Monitoring System of the American Medical Association, estimates of the number of full-time equivalent physicians actually in practice in the two states and the comparative productivity of those physicians were made. Based on the state-level data, the estimates of actively practicing physicians are approximately 14 percent lower than the head-count number in North Carolina and, by using a more conservative estimation method, are approaching a 10 percent lower number than the head-count number in Washington. Using national productivity data, the effective supply of nonmetropolitan physicians appears to have not grown significantly over the past 10 years, and for family physicians the supply has declined by 9 percent. These estimates of the effective physician supply support long-held claims that rural communities continue to experience a severe undersupply of practitioners. These results suggest that the way in which physicians are counted needs to be re-examined, especially in rural places where the ratios of providers to population are more sensitive to small changes in supply.