Structural and functional changes observed in the aging kidney predispose the elderly patient to acute renal failure. Up to 36% of the patients with acute renal failure from this institution were over 70 yr, and the literature is full of similar experiences. The elderly patient with abrupt cessation of adequate renal function requires a special work-up in diagnosis and treatment. Prerenal and obstructive causes are of particular interest. Although the question of whether or not age has an independent prognostic importance during an episode of acute renal failure remains debated; when these and other authors compared the outcome of young and old populations with these disorders, a similar evolution was always observed. Age should not be used as a discriminant factor in therapeutic decisions concerning acute renal failure.