Motivated by a search for improved quality and efficiency, increasing numbers of hospitals and physicians are moving from systems in which all primary care providers manage their own hospitalized patients or rotate this responsibility among themselves at infrequent intervals to voluntary or mandatory systems in which patients are "handed off" to the care of an inpatient physician, the "hospitalist." All hospitalists manage medical patients in the hospital. Other potential roles for these physicians include triage in the emergency department, transfer of "out-of-network" patients, management of patients in the intensive care unit, preoperative and postoperative management of surgical patients, and leadership in hospital quality improvement and regulatory work. Hospitalists may add value by being more available to inpatients, having more hospital experience and expertise, and having an increased commitment to hospital quality improvement compared with primary care providers. Potential disadvantages of the hospitalist model include loss of information as a result of discontinuity of care, patient dissatisfaction, loss of acute care skills by primary care physicians, and burnout among hospitalists. A variety of models of care are needed to meet the clinical, organizational, financial, and political demands of diverse health care systems. The favored model should be that which produces the best clinical outcomes and the highest patient satisfaction at the lowest cost.