The impact of a required preceptorship program was measured by comparing the perceptions of senior medical students who would have elected the preceptorship rotation had it not been required (the elective group) and those who participated only to fulfill the requirement (the required group). The main difference between the two groups before the preceptorship was the elective group's career preference for family medicine and the required group's preference for an internal medicine subspecialty. The preceptorship had no impact for either group on inclinations toward other specialties, preferred practice setting, or assessment of practice location determinants. Both groups, however, perceived an increase in knowledge of primary care practice and confidence in relevant clinical skills following the preceptorship. These results are used to support the value of a required preceptorship program.