Using data for 1975 to 1985 from the Area Resource File (ARF), net number changes in different age groups of physicians practicing in nonmetropolitan counties are examined. Small net increases are seen in the higher age groups in most county size categories but the most striking change is large increases in the age groups up to age 44. Family practitioners show a net decline in all county size categories for ages 45-54, but these are offset by increases in medical specialists. In counties of less than 25,000 population, the rate of turnover of physicians over the 1983-1988 period was 25 percent; physicians exiting these counties had a mean age of 52.3 years. The data indicate that aging of physicians in rural counties should not affect maintenance of current supply in the short run, but that increasing the physician-to-population ratio in areas with less adequate supply will be difficult, particularly if the rate of increase of younger physicians in nonmetropolitan counties does not continue.