In recent years the mortality rate in patients with acute renal failure has been reduced to between 40% and 50%. Dialysis, particularly when used early, and better management of fluid and electrolyte abnormalities account for the improved statistics. This report analyzes the cause of death in the non-surviving patients, most of whom were treated with hemodialysis or peritoneal dialysis under good clinical conditions. During the 12 years ending Dec. 31, 1961, among the patients with acute renal failure treated by the Renal and Electrolyte Division of Georgetown University Hospital, exactly 100 died and were autopsied. The series is limited to those who were autopsied in order to verify the diagnosis and provide precise information concerning the cause of death. Chronologically, the first 8 patients were treated before the establishment of the Renal Laboratory, but are included for completeness since they underwent hemodialysis. Subsequently all were treated by one of us,