PURPOSE: To compare first- and fourth-year medical students' opinions about primary care practice. METHOD: A cross-sectional survey was made of medical students at New York Medical College (NYMC) and East Carolina University School of Medicine (ECUSOM) over three years (1993-94, 1994-95, and 1995-96). Three consecutive classes of first-year students from both schools (n = 807), two consecutive classes of fourth-year NYMC students (n = 373), and three consecutive classes of fourth-year ECUSOM students (n = 221) were given a self-administered questionnaire about professional aspects of primary care practice. Responses to ten items about primary care practice were the independent variables in a logistic regression analysis. Career choice, categorized as primary care or non-primary care, was the dependent variable. Independent, two-tailed t-tests were employed to compare the responses of the first-year students interested in primary care careers with those of the fourth-year students interested in primary care careers. RESULTS: In all, 639 (79%) of the first-year students and 396 (67%) of the fourth-year students returned completed questionnaires. The first-year students interested in primary care careers were significantly more likely to believe that primary care practice has more prestige, has more intellectual stimulation, needs a large knowledge base, and involves work that is more important than that of non-primary care physicians, and were significantly more likely to disagree with the assertion that in primary care practice, physicians have more control over their working hours. With one exception (prestige of primary care practice), all these independent variables were significant for the fourth-year students as well. The comparison of the first- and fourth-year students indicated that the fourth-year students were significantly more likely to believe that primary care practice has more intellectual stimulation, needs a large knowledge base, and requires knowledge that non-primary care practice may not; they were also significantly more likely to disagree with the assertions that primary care practice is adequately compensated, has more prestige, and allows more control over working hours. CONCLUSION: It appears that students' positive perceptions about primary care practice may change as realistic perceptions about the professional demands on primary care physicians develop during medical school.