The authors compared charges for ambulatory and continuing patient care prescribed by residents in internal medicine and family medicine. An analysis of covariance showed that the charges per encounter in internal medicine were $38.83 greater than charges in family medicine after accounting for differences such as patient age, diagnosis, and severity of condition. However, family practitioners scheduled patient encounters more frequently. The median number of days between encounters was 30 for family medicine and 60 for internal medicine. The duration of medical care for each patient (up to 18 months was possible) and the summation of encounter charges over that duration of medical care were evaluated. Because only two out of eight duration-of-medical-care categories were significantly less in family medicine, the differences in charges between the specialties essentially disappeared. Comparative studies which consider only charges per encounter potentially have a large bias.