BACKGROUND Studies have examined factors affecting medical students' specialty choice, but little research exists on stability of these specialty interests. OBJECTIVE To describe patterns of change in specialty interests during medical school and examine associations between specialty change patterns and gender, desire for a high-prestige career, and interest in prevention. METHODS Medical students (Class of 2003) at 15 representative US schools were invited to complete surveys during freshman orientation, entry to wards, and senior year. METHODS This analysis used data from 942 students who completed all 3 surveys. METHODS In addition to a number of other items, students were asked to choose the 1 specialty they were most interested in pursuing. RESULTS The most common specialty choices among freshman students were pediatrics (20%) and surgery (18%); least common choices were psychiatry and preventive medicine (1% each). General internal medicine was the initial specialty choice for 8%. Most students changed their specialty choices, regardless of initial interest. Only 30% of those initially interested in primary care (PC) remained interested at all 3 time points, compared to 68% of those initially interested in non-PC. Female versus male students were more commonly interested in PC at all 3 time points. Senior students interested in non-PC specialties were more likely to desire a high-prestige career (48%) than those interested in PC (31%). CONCLUSIONS Medical students may benefit from more intensive introduction to some specialties earlier in pre-medical and medical education. In addition, increasing the prestige of PC fields may shape the physician workforce.