SUMMARY The use of aprotinin in cardiac surgery to reduce perioperative bleeding and transfusion is controversial. We assessed the effect of aprotinin on the risk of acute renal failure in 423 patients who underwent on pump cardiac surgery between January 1, 2005 and December 31, 2006. Of these 423 patients, 318 (75.2%) received aprotinin (median dose=3.0 million KIU, standard deviation=2.8 million KIU; interquartile range: 2 million KIU to 4 million KIU). Aprotinin was more likely to be used in patients who did not cease aspirin before surgery, in urgent or emergency surgery, who had impaired left ventricular function, a longer period of bypass and aortic cross-clamp time, and with both coronary artery bypass graft and valvular surgery performed. The overall incidence of acute renal failure requiring dialysis was 2.8%. The use of aprotinin was not associated with a reduction in transfusion nor an increased risk of renal failure requiring dialysis, atrial fibrillation, cerebrovascular accident or mortality in the univarate analyses. In the multivariate analysis, only preoperative serum creatinine concentration (odds ratio [OR] 1.06 per 10 [micro]mol/l increment in creatinine, 95% confidence interval [CI]. 1.01 to 1.14, P=0.029) and urgency of the surgery (urgent vs. scheduled surgery. OR 12.8, CL. 2.3 to 70.8, P=0.004; emergency vs. scheduled surgery: OR 23.1, CL 3.0 to 180.2, P=0.003) were significantly associated with an increased risk of acute renal failure requiring dialysis. The use of low-dose aprotinin did not significantly reduce perioperative transfusion requirements and was not a significant risk factor for acute renal failure requiring dialysis in our patients.