Background-The outcome for children with acute renal failure (ARF) may be poor. However, relatively few published studies have considered prognosis of these patients. Methods-We prospectively studied, from 1978 to 1998, 92 such children without heart disease to try to identify risk factors for mortality. Results-Forty five per cent of children with tumours, shock, and other causes died compared with none of those with a primary urinary tract related problem. ARF did not seem to be the cause of death in any case. Univariate analysis showed that in the non-primary urinary problem group (55 cases), patients with hypotension, high values of BUN or creatinine, or who needed mechanical ventilation or dialysis, had a poor outcome. Multivariate analysis showed that probability of death can be estimated using the following score: -0.02 + 0.28 (hypotension) + 0.19 (ventilation) + 0.27 (dialysis) + 0.01 (BUN). Conclusions-Mortality of patients with ARF was related to aetiology, the need for dialysis and/or ventilator use, hypotension, and BUN values.