A large proportion of hospital stays stem from rapid readmission of elderly patients. These patients represent high cost users of inpatient care. Intervention in the hospital admission-readmission cycle may serve the interests of patients and payors alike. Data collected through comprehensive geriatric assessment can be useful in identifying those patients at high risk of readmission and who might benefit from more intensive in-hospital or post hospital attention. However, risk factors for readmission are largely unknown. We conducted a prospective study of elderly patients admitted to a metropolitan teaching hospital medical service and assessed by a geriatric team, to increase our knowledge of the factors associated with hospital readmissions. The most powerful predictor of hospital readmission within 6 months proved to be prior hospitalization. Attempts to reduce rehospitalizations in elderly patients must focus on those with prior recent hospitalizations.