Between February and September 2003, 136 (5.3%) of 2,558 patients undergoing cardiac surgery were supported with intra-aortic balloon counterpulsation. There were 71 infected (group 1) and 65 noninfected (group 2) patients. Risk factors for nosocomial infections were identified by univariate and multivariate analysis. On univariate analysis, significant risk factors were operation time, balloon pump duration, ventilation hours, duration of central venous catheter placement, amount of blood transfused, left ventricular ejection fraction<30%, intra- and/or postoperative intra-aortic balloon counterpulsation, surgery under cardiopulmonary bypass, combined procedures, re-exploration, and Acute Physiology And Chronic Health Evaluation (APACHE) II score. On multivariate analysis, ventilation hours and amount of blood transfused were independently associated with group 1. Respiratory tract infections were common in the balloon counterpulsation population (41.1%). Mortality was significantly higher in patients needing balloon pump support (19.9%) compared to controls (1.1%), but it was similar in groups 1 and 2. Recognition of risk factors for postoperative infection in patients undergoing cardiovascular surgical procedures with intra-aortic balloon counterpulsation may help to improve their prognosis and allow more organized surveillance.