This study was conducted to examine factors used by medical students to select a primary care specialty that may differentiate students who choose the primary care specialties of family medicine, internal medicine, pediatrics, and combined internal medicine-pediatrics.A questionnaire was sent to all family physicians and an equal number of other primary care physicians graduating from one of 24 medical schools in 1997-1999. Twelve schools had increasing proportions of graduates choosing family medicine in this study period, and 12 had decreasing proportions. The questionnaire asked about factors related to choice of specialty, which could be grouped into the specialty domains of type of patients, process, content, and setting.For family physicians, the most important factor was patient relationships, and the second most important was wanting an approach to the practice of medicine similar to that of family physicians. Internists indicated as most important wanting to work with adults and as the next most important an "internal medicine approach" to the practice of medicine. Most important for pediatricians was working with children and next most important was having patient relationships like other pediatricians. Those in combined internal medicine-pediatrics most often indicated a desire to work with children and next most important was an approach to medicine like others in their specialty.The most important reasons for choice of specialty were similar for all primary care specialties and related to congruence between the graduate and the physicians in the specialty or the process of providing care within that specialty. The factors that differentiated the four specialties related to the content of the specialty.