OBJECTIVES: This study examined the relative and incremental importance of multiple predictors of generalist physicians' care of underserved populations. METHODS: Survey results from a 1993 national random sample of 2955 allopathic and osteopathic generalist physicians who graduated from medical school in 1983 or 1984 were analyzed. RESULTS: Four independent predictors of providing care to underserved populations were (1) being a member of an underserved ethnic/minority group, (2) having participated in the National Health Service Corps, (3) having a strong interest in practicing in an underserved area prior to attending medical school, and (4) growing up in an underserved area. Eighty-six percent of physicians with all 4 predictors were providing substantial care to underserved populations, compared with 65% with 3 predictors, 49% with 2 predictors, 34% with 1 predictor, and 22% with no predictors. Sex, family income when growing up, and curricular exposure to underserved populations during medical school were not independently related to caring for the underserved. CONCLUSIONS: A small number of factors appear to be highly predictive of generalist physicians' care for the underserved, and most of these predictive factors can be identified at the time of admission to medical school.