BACKGROUND: Acutely ill older persons often experience adverse events when cared for in the acute care hospital. OBJECTIVE: To assess the clinical feasibility and efficacy of providing acute hospital-level care in a patient's home in a hospital at home. DESIGN: Prospective quasi-experiment. SETTING: 3 Medicare-managed care (Medicare + Choice) health systems at 2 sites and a Veterans Administration medical center. PARTICIPANTS: 455 community-dwelling elderly patients who required admission to an acute care hospital for community-acquired pneumonia, exacerbation of chronic heart failure, exacerbation of chronic obstructive pulmonary disease, or cellulitis. INTERVENTION: Treatment in a hospital-at-home model of care that substitutes for treatment in an acute care hospital. MEASUREMENTS: Clinical process measures, standards of care, clinical complications, satisfaction with care, functional status, and costs of care. RESULTS: Hospital-at-home care was feasible and efficacious in delivering hospital-level care to patients at home. In 2 of 3 sites studied, 69% of patients who were offered hospital-at-home care chose it over acute hospital care; in the third site, 29% of patients chose hospital-at-home care. Although less procedurally oriented than acute hospital care, hospital-at-home care met quality standards at rates similar to those of acute hospital care. On an intention-to-treat basis, patients treated in hospital-at-home had a shorter length of stay (3.2 vs. 4.9 days) (P = 0.004), and there was some evidence that they also had fewer complications. The mean cost was lower for hospital-at-home care than for acute hospital care (5081 dollars vs. 7480 dollars) (P < 0.001). LIMITATIONS: Possible selection bias because of the quasi-experimental design and missing data, modest sample size, and study site differences. CONCLUSIONS: The hospital-at-home care model is feasible, safe, and efficacious for certain older patients with selected acute medical illnesses who require acute hospital-level care.