In a retrospective study, 47 patients with acute renal failure following cardiovascular surgery were evaluated in the Cardiovascular Surgery ICU of the University Hospital, Zurich, from 1991 to 1994. The object of the study was to investigate the contribution of hemofiltration for acute renal failure following cardiovascular surgery. The aim was further to identify risk factors which impair survival. We found that overall mortality was 70.2%, but was influenced by the patients' age. In patients under 60 (n = 9) the mortality rate was 55.6%; in patients from 60 to 69 (n = 19) the mortality rate was 57.9%. However, in patients aged 70 and over (n = 19), there was an increase in mortality to 89.5%. Specifically, the outcome was tested in a stepwise logistic regression and we found that recovery of renal function following hemofiltration was the most important factor favoring survival (p < 0.001). Further statistical analysis revealed that age 70 years or over was one of the main risk factors leading to death (p < 0.03), whereas preoperative renal insufficiency had no influence on postoperative outcome (p < 0.29). We conclude that postoperative renal function represents the crucial factor in survival. Although hemofiltration achieved adequate results in all groups, the patients of 70 years and more experienced a significantly higher mortality rate. This suggests that the increased mortality of the elderly was not due to renal failure in itself but rather was related to polymorbidity. Hence we propose that in the latter group of elderly patients candidates for hemofiltration are to be very carefully selected, particularly if they have additional complications.