We have reviewed all patients in a critical care unit who required dialysis for acute renal failure during a five year period from 1981-5. There were 45 patients, all of whom were severely ill, the majority requiring mechanical ventilation. Twenty-five were classified as surgical, including trauma, eighteen medical and two obstetric. The overall mortality rate was 53%. A wide range of variables were reviewed and it was found that only the number of failed organs was a significant predictor of mortality. Progressive multiple organ failure in turn was associated with ineradicable sepsis in the majority, although in 25% of deaths with multiple organ failure, sepsis was not proven. Patients without sepsis or multiple organ failure had excellent survival. Further reductions in the acute renal failure mortality rate will depend on better methods of prevention, diagnosis, and management of sepsis.