PURPOSE: Medical students' career choices affect health care. To understand how to increase the number of students who choose careers in internal medicine (IM), students who seriously considered IM but chose another field ("Switchers") and those who rejected IM ("Never Considered") were compared with those who chose IM ("Choosers"). METHOD: Fourth-year medical students from 11 U.S. institutions were surveyed about demographics, medical school educational experiences, and aspects of the specialty of IM. Univariate analysis and multivariate logistic regression models examined associations between student characteristics and classification as Switchers, Choosers, and Never Considered. RESULTS: A total of 1,177 students completed the survey (82% response rate). There were 274 (23%) Choosers, 398 (34%) Switchers, and 499 (43%) Never Considered. The authors' models explained over 80% of variance in these three career choice classification groups. For most responses, an increasingly favorable gradient from Never Considered to Choosers was observed. Multivariate analysis revealed six items that were associated with higher probability of choosing IM: types of patients internists see, timing of career decision, interest groups, intellectual challenge, satisfaction among internists, and the core IM clerkship. CONCLUSIONS: Several potentially modifiable educational experiences and aspects of IM distinguished Switchers from the other two groups. The percentage of variance explained by group suggests that these findings identify important underpinnings of career decisions. These items also suggest ways that educational experiences and aspects of the specialty could be redesigned by academicians and policy makers to improve the attractiveness of IM careers.