BACKGROUND: Half of patients admitted to hospital for reasons unrelated to childbirth are age 65 years or older. Nonetheless, few hospital-based physicians have received training in geriatric medicine, and few geriatricians practice in the hospital. This paper describes the state of the science of hospital care for older patients, and identifies opportunities and barriers to improving their care. METHODS: General medical journals from 1980 to the present were selectively reviewed to identify original articles on the treatment of specific diseases and syndromes on hospitalized persons age 65 years or older. Information was synthesized to describe the course of these patients during and after hospitalization, and to identify effective management strategies and gaps in knowledge. RESULTS: Older persons in hospitals pose substantial clinical challenges: they have high rates of cognitive impairment, delirium, disability, and difficulty walking, and they often require increased attention, longer lengths of stay, and higher hospital costs than younger patients with the same diagnoses. Disease-specific interventions have not been studied extensively in those older than 75 years. Multicomponent interventions can reduce short-term rates of disability and delirium without increasing costs, but they have not been widely disseminated. Interventions to treat or prevent other common conditions in hospitalized older patients have not been proven effective. CONCLUSIONS: Fundamental discoveries in the science of hospital medicine are needed to prevent or treat geriatric syndromes, to treat common diseases in the very old, and to put into practice what is known. Hospital-based physicians can address these gaps in knowledge and practice with geriatricians, building from their shared perspectives on the care of the aged in complex health systems. (c) 2006 Society of Hospital Medicine.