The case mix of patient caseloads of nurse practitioners (NPs), faculty attending physicians (F/MDs), and resident housestaff in an inner-city teaching hospital was examined. Social and demographic variables as well as diagnoses, medications, risks, and functional status were used to define complexity. Charts of 111 patients (37 per group) were analyzed. Patients of NPs and F/MDs were essentially equally complex, but residents' patients were somewhat less complicated. Differences in styles of practice were seen, with NPs attending more to symptoms of nonpathological conditions, comfort, and comprehensiveness of care. Scope of practice, complexity, and system of care are suggested as important variables to consider in future studies of NPs and in studies relating case mix to productivity and resource consumption.