The aim of this study was to provide a broad characterization of the epidemiology of acute renal failure (ARF) in the United States using national administrative data and describe its impact on hospital length of stay (LOS), patient disposition, and adverse outcomes. Using the 2001 National Hospital Discharge Survey, a nationally representative sample of discharges from nonfederal acute care hospitals in the United States, new cases of ARF were obtained from hospital discharge records coded according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). Multivariate regression analyses were used to explore the relation of ARF to hospital LOS and mortality as well as discharge disposition. Review of discharge data on a projected total of 29,039,599 hospitalizations identified 558,032 cases of ARF, with a frequency of 19.2 per 1000 hospitalizations. ARF was more commonly coded for in older patients; men; black individuals; and the setting of chronic kidney disease, congestive heart failure, chronic lung disease, sepsis, and cardiac surgery. ARF was associated with an adjusted prolongation of hospital LOS by 2 d (P < 0.001) and an adjusted odds ratio of 4.1 for hospital mortality and of 2.0 for discharge to short- or long-term care facilities. In a US representative sample of hospitalized patients, the presence of an ICD-9-CM code for ARF in discharge records is associated with prolonged LOS, increased mortality, and, among survivors, a greater requirement for posthospitalization care. These findings suggest that in the United States, ARF is associated with increased in-hospital and post-hospitalization resource utilization.