Care of hospitalized patients by "hospitalists" -- often defined as physicians who dedicate at least 25% of their practice to inpatient care -- is a recent, growing, and controversial trend in health care delivery in the United States. But despite the growth of interest in hospitalists, there have been few scientific evaluations of the concept. The comprehensive aim of this research study is to measure and analyze the effects of hospitalists on patient outcomes, costs and medical education on the general medical services of a group of academic centers.