The probability of death in patients with acute renal failure (ARF) remains high. A valid prognostic index available on patient admission and during follow-up could be helpful for decision making. In this study, 94 ARF patients requiring dialysis (not responding to a previous single dose of furosemide 15 mg/kg) were included. On admission, patients were classified according to a Simplified Acute Physiology Score (SAPS) of < or = 15 or > 15. The prognostic value of 11 risk factors was analyzed. Only 6 in 11 risk factors were significant by univariate analysis: age (> 55 years) (0.02), mechanical ventilation (0.008), oliguria (< 500 mL/day during the first 5 days) (0.02), sepsis (0.001), shock (0.007), and serum bilirubin (> 30 mumol) (0.001). Only oliguria and sepsis were significant risk factors by multivariate analysis. Overall mortality rate was 41%. Mortality rate was higher in patients with SAPS > 15 (65%) than in those with SAPS < or = 15 (22%) (0.001). Patients with > 3 risk factors showed a significantly higher mortality rate than patients with < 3 risk factors (all patients disregarding SAPS) (0.001). Considering the worst combination of risk factors by univariate analysis, mortality prediction was 56% if oliguria, sepsis, and high serum bilirubin were present, and reached 80% if an older age was added (four risk factors). Ventilation increased probability of death to 92% (five risk factors). If all six risk factors were present, the probability rose to 96%. The corresponding observed mortality rate was 32% for three risk factors, 70% for four, 81% for five and 100% for six risk factors. The results suggest that probability of death in ARF requiring dialysis can be correctly estimated when more than three significant risk factors are present. If confirmed, they could avoid using a more complex severity scoring system in patients with ARF requiring dialysis.