OBJECTIVE To assess the effect of an ambulatory care experience on medical students' perceptions of internal medicine and their choices of careers (as measured by residency selections). METHODS In 1990-91, the 196 third-year students enrolled in the 12-week internal medicine clerkship at the University of Texas Medical School at San Antonio were randomized to a curriculum that included a three-week ambulatory care component or to a traditional, exclusively inpatient curriculum. The ambulatory curriculum included the evaluation of walk-in-patients, exposure to community internists, and a lecture series. The students' perceptions of internal medicine were surveyed before and after the clerkship. Their career choices were determined by their residency selections at graduation. Data analysis employed chi-square tests, t-tests, and logistic regression. RESULTS Of the 196 students, 184 (76 in the ambulatory and 108 in the traditional curricula) provided complete data. The ambulatory care students were somewhat more likely to enter an internal medicine residency (odds ratio = 1.49; 95% CI, 0.72 to 3.09) than were the traditional students. The ambulatory care students' perceptions of internal medicine did not change significantly from before to after the clerkship. CONCLUSIONS The ambulatory curriculum had a modest but favorable effect on the students' selections of careers in internal medicine, but was not associated with changes in their perceptions of internal medicine.