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.