Postgraduate medical education underwent substantial change during the 1970s: medical-school classes grew, the internship year was eliminated, and the numbers of M.D.s entering primary-care specialties increased. The purpose of this study is to develop a planning model of graduate medical education that can project the impact of these and other changes on the numbers and specialty mix of physicians completing training. The model is applied to an analysis of trends in graduate medical education and to the probable consequences of policy recommendations made by the Graduate Medical Education National Advisory Committee (GMENAC). The results show that the trend toward increasing percentages of M.D.s entering primary-care specialties from 1970 to 1976 changes to no increase from 1976 to 1980. Thus, the GMENAC policy recommendation to increase primary care further is not likely to occur spontaneously in the near future.