Open-heart surgery was performed on 1686 adult patients between 1980 and 1984. The patients were operated on using cardiopulmonary bypass procedures (CPB). Fifteen patients developed acute renal failure (ARF) after CPB, i.e. the incidence of ARF was 0.9%. All these patients were treated by peritoneal dialysis or haemodialysis. Pre-operative possible risk factors in the ARF group were compared to those in a control group of 30 patients (15 consecutive coronary artery bypass grafting and 15 consecutive valve repair procedures) experiencing no complications. Age, New York Heart Association (NYHA) classification, ejection fraction, cardiac volume and left ventricular end-diastolic pressure were not risk factors for the development of renal failure. The incidence of thrombocytopenia after CPB was statistically significantly different between the control and ARF groups. The mortality from ARF was 66.6%. The causes of death were peri-operative myocardial infarction, infection and gastrointestinal bleeding. CPB time, perioperative events and postoperative infection were the main factors contributing to ARF. Renal failure was twice as common in valve procedures as in coronary artery revascularization procedures. Impairment of renal function proved reversible only in those patients who survived. After restoration of renal function the prognosis was good.