AIM: To clarify the incidence and nature of postoperative hyperbilirubinemia in patients after mod extracorporeal circulation, to analyze possible perioperative risk factors, and to elucidate the clinical significance of postoperative hyperbilirubinemia associated morality and morbidity.METHODS: Between March 2005 and May 2006, three hundred and eighty six consecutive patients undergoing extracorporeal circulation surgery due to a variety of cardiac lesions were investigated prospectively. The incidence of postoperative hyperbilirubinemia was defined as a serum total bilirubin concentration of more than 51 μmol/L. Several perioperative parameters were compared by logistic regression between hyperbilirubinemia and non-hyperbilirubinemia patients to determine possible risk factors contributing to postoperative hyperbilirubinemia and mortality.RESULTS: Overall incidence of postoperative hyperbilirubinemia was 25.3% (98/386). In patients with postoperative hyperbilirubinemia, 56.2%reached peak total bilirubin concentration on the first postoperative day, 33.5% on the second day, and 10.3%on the seventh day. Eighty percent of the increase of total bilirubin resulted from an increase of both conjugated and unconjugated bilirubin. Development of postoperative hyperbilirubinemia was associated with a higher mortality (P ＜ 0.01), longer duration of mechanical ventilation (P ＜ 0.05) and longer ICU stay time (P ＜ 0.05). Preoperative total bilirubin concentration, preoperative right atrium pressure,numbers of valves replaced and of blood transfusion requirement were identified as important predictors for postoperative hyperbilirubinemia.CONCLUSION: Early postoperative hyperbilirubinemia after mod extracorporeal circulation is mainly caused by an increase in both conjugated and unconjugated bilirubin, and is associated with a high mortality.Important contributing factors are the preoperative total bilirubin concentration, preoperative severity of right atrial pressure, numbers of valve replacement procedures, and the amount of blood transfusion requirement during and shortly after surgery. We suggest that postoperative hyperbilirubinemia is a multifactorial process, which is caused by .both the impaired liver function of bilirubin transport and the increased production of bilirubin from haemolysis.