Introduction. Acute renal failure is a frequent complication following cardiac surgery, with influence on postoperative morbidity and mortality. Objective. Our study aims to evaluate the prevalence of those factors which have a role in the developement of the acute renal failure. Material and methods. We studied the patients operated in 2006 at the Cardiovascular Surgery in Tg-Mures, studying all risk factors which play a role in the appearence of the renal failure. Results and discussion. We studied 690 patients, from which 46 patients (6,5%) developed renal failure, 14 patients required continuous dialysis, 6 peritoneal dialysis. Patients with acute renal failure had more frequently associated coagulopathy, hematemesis, metabolic disturbances, neurologic dysfunction. Conclusions. Acute renal failure developed more frequently in patients with low cardiac output, after long cardiopulmonary bypass, at extreme ages and was associated with a high postoperative morbidity and mortality.