Five hundred twenty new patients were randomly and prospectively assigned to receive their care in the Internal Medicine Clinic or Family Practice Clinic of a large university hospital. The patients were followed by residents in training under the supervision of board-certified internists or family physicians. After a mean length of care of slightly over two years, the charts were reviewed for frequency of visits to primary care providers (internal medicine or family practice), Emergency Room, Acute Care Clinic, and all clinics other than the two primary care clinics. The records were also reviewed for laboratory tests ordered. Frequency of visits to the clinic of primary care, Emergency Room, Acute Care Clinic, and broken appointments were all significantly higher for patients randomized to the Internal Medicine Clinic. In addition, the median total annual cost of laboratory tests for patients followed by internal medicine physicians was significantly higher, largely because of higher laboratory charges generated by the specialist consultants. Over the study period, internal medicine patients had a significantly higher number of visits to all nonprimary care clinics and specifically to the dermatology, obstetrics and gynecology, and general surgery consultant clinics. It can be concluded that in this clinical environment, the practice styles of internal medicine and family practice are different.