In this retrospective study, 287 patients with acute renal failure observed between 1980 and 1985 were divided into 2 groups, according to age: group 1 of 65 years or more (n = 100) and group 2 between 17 and 64 years (n = 187). In both age groups the whole spectrum of causes of acute renal failure was found, but within that spectrum a higher incidence of post-renal failure, acute renal vascular disease and of hypovolaemic acute renal failure was noted in group 1 versus group 2. On the other hand, pigment-induced acute renal failure was lower in group 1 (4%) versus group 2 (13%). The overall survival was 54% in the elderly versus 56% in the younger patients (NS). A close relationship between survival and the number of postadmission complications was found in both groups. Interestingly, the presence of severe hypokalaemia (less than 3.5 mmol/l) and metabolic alkalosis (plasma HCO3 greater than 30 mmol/l) was associated with a very high mortality of 73% and 86% respectively in the elderly patients. Complete or incomplete recovery of renal function was the same in both age groups. It is concluded that age alone should not be used as a discriminating factor in therapeutic decisions concerning acute renal failure in an older patient.