Two hundred and forty-two elderly patients (> 65 years) with acute renal failure (ARF) treated at a predominantly medical intensive care unit between 1975 and 1990 were retrospectively analyzed for underlying diseases, severity of disease (as evaluated by the rate of ventilated patients, septicemia and APACHE II score, respectively), causes of ARF, acute and chronic risk factors for the development of ARF, complications during treatment and outcome. Overall mortality was 61%; 28 patients (12%) died in spite of resolution of ARF so actually, 49% of the patients died in ARF. Outcome was comparable to other age groups with overall mortality being 57% in patients < 18 years and 59% in those 19-65 years. Moreover, within the group of elderlies mortality did not increase with age and was 60% in those aged 65-68 and 54% in those aged > 80 years, respectively. The need for renal replacement therapy, plasma creatinine > 6 mg/dl, anuria, BUN > 120 mg/dl, ventilator dependency and the presence of septicemia all negatively affected outcome. During the years 1975 to 1990 mortality decreased from > 70% to < 50% (p < 0.02). This improvement of survival was seen in spite of an increase in the severity of disease (1975-1982: 20% ventilated patients, 24% with septicemia, 1983-1990 51% and 40%, respectively, p < 0.01). We conclude that age per se is not an important determinant of survival in patients with ARF and that prognosis has improved considerably during the last 15 years and this was seen in spite of an increase in the severity of disease. It is not justified to withhold therapy in elderly patients acquiring ARF.