Two hundred and fifty consecutive patients with acute renal failure treated by continuous haemofiltration on one intensive care unit (ICU) were studied prospectively to investigate the possibility of predicting outcome at the time of referral. Logistic regression analysis was used to identify important prognostic factors and the regression coefficients were used to weight a scoring system for the severity of illness of patients with acute renal failure. Overall survival was 53% with improvement over the course of the study. Multivariate analysis showed that outcome was related to age, need for artificial ventilation, use of inotropes, urine volume, serum bilirubin, arterial base deficit and serum creatinine. The scoring system based on the first five of these variables had a specificity of predicting death of 67% and a sensitivity of 76%.