Of 1988 patients who underwent open-heart surgery from 1980 through 1988, 68 (3.4%) developed postoperative acute renal failure requiring dialysis (2.5% of adult and 8.3% of pediatric patients). Isolated aortocoronary bypass grafting was the operation with lowest incidence of this complication (0.6%). Acute renal failure usually appeared during the first 3 postoperative days. It carried a mortality rate of 63%, with half of the deaths occurring during the first few postoperative days, due to low cardiac output and progressive multiple organ failure. Logistic regression analysis in cases of aortic valve replacement demonstrated that significant independent preoperative risk factors for acute renal failure were renal insufficiency (serum creatinine greater than 110 mumol/l in greater than or equal to 2 samples) and increased cardiothoracic index/left ventricular end-diastolic dimension. Data from the literature indicated no time-related trend towards reduction of acute renal failure incidence or mortality. Prevention of low cardiac output is of major importance in these respects. Operative intervention before development of advanced disease with left ventricular dilatation and secondary kidney failure is advocated.