Although patients with acute renal failure (ARF) are now older and sicker than in the past, mortality remains constant or even slightly lower, which suggests a better management of the syndrome. Several clinical conditions, mainly assisted respiration, hypotension, oliguria, coma and jaundice, have a detrimental effect on outcome. Previous health status, original disease, a hospital and/or ICU start of the ARF, and age of the patient also seem to affect outcome of these patients. ARF observed in the ICU setting has a poorer prognosis than the ARF treated in other hospital areas. This is because of the higher number of associated organ failures observed in the ICU. Estimation of outcome could be done either using specific ARF or general ICU score systems. They allow risk stratification of the patients, and some of them give an individual prognosis that at present should not be used for a withdrawal decision. Functional outcome of ARF is usually good, although some patients need to be maintained on chronic dialysis.