Context: Physician supply is anticipated to fall short of national requirements over the next 20 years. Rural areas are likely to lose relatively more physicians. Policy makers must know how to anticipate what changes in distribution are likely to happen to better target policies. Purpose: To determine whether there was a significant flow of physicians from urban to rural areas in recent years when the overall supply of physicians has been considered in balance with needs. Methods: Individual records from merged AMA Physician Masterfiles for 1981, 1986, 1991, 1996, 2001, and 2003 were used to track movements from urban to rural and rural to urban counties. Individual physician locations were tracked over 5-year intervals during the period 1981 to 2001, with an additional assessment for movements in 2001-2003. Findings: Approximately 25% of physicians moved across county boundaries in any given 5-year period but the relative distribution of urban-rural supply remained relatively stable. One third of all physicians remained in the same urban or rural practice location for most of their professional careers. There was a small net movement of physicians from urban to rural areas from 1981 to 2003. Conclusions: The data show a net flow from urban to rural places, suggesting a geographic diffusion of physicians in response to economic forces. However, the small gain in rural areas may also be explained by programs that are intended to counter normal market pressures for urban concentrations of professionals. It is likely that in the face of an overall shortage, rural areas will lose physician supply relative to population.