Operative risk stratification scales for use in cardiac surgery have been developed for patients who undergo procedures using extracorporeal circulation. The aims of the present study were to investigate the use of six preoperative risk stratification scales in patients undergoing beating-heart surgery and to identify risk factors for major complications and mortality in our group of patients who underwent revascularization using this approach. Between January 1997 and December 2002, we performed 762 coronary artery bypass operations on the beating heart; 61 patients suffered major complications (8%) and 25 died (3.3%). Risk factors for major complications and death were identified using logistic regression analysis of prospectively collected data. The following risk scores were calculated for each patient: Parsonnet 95, Parsonnet 97, Euroscore, Cleveland, Ontario, and French. Receiver operating characteristic curves were used to compare the ability of each scale to predict mortality and major complications. In our patient group, the preoperative variables associated with increased risk were: need for cardiopulmonary resuscitation, renal dysfunction, peripheral vasculopathy, and the presence of severe left main coronary artery disease, three-vessel disease, or an impaired ejection fraction. Mortality and major complications were best predicted by the Parsonnet 95 and Euroscore scales.