Increasing numbers of U.S. citizens are studying medicine abroad and returning for graduate medical education and practice. The numbers and performance of U.S. citizen and all other graduates of foreign medical schools on the certifying examination of the American Board of Internal Medicine were compared with those of graduates of U.S. medical schools for 1975-1980. Numbers of first-taker U.S. citizen foreign medical school graduates increased whereas numbers of all other foreign medical school graduates decreased during this period. In 1980, U.S. citizens represented 19 percent of all first-taker foreign medical school graduates. During the study period, annual examinations were passed by 79 to 82 percent of U.S. medical school graduates, 15 to 38 percent of U.S. citizen foreign medical school graduates, and 27 to 45 percent of all other foreign medical school graduates taking an examination for the first time. On each examination, U.S. citizen foreign medical school graduates did not do as well as all other foreign medical school graduates. Members of all groups met the same postdoctoral training requirements.