Background: Renal dysfunction is common after cardiac surgery, ranging from minor changes in serum creatinine without clinical manifesta- tions to frank anuria and severe metabolic dysfunction. In recent years two scores were developed to diagnose renal dysfunction. The aim of our study was to compare the prognostic value of these scores in acute renal failure associated with cardiac surgery. Materials and methods: In our prospective clinical observational study we calculated and compared the AKIN (Acute Kidney Injury Network) and RIFLE (Risk, Injury, Failure, Loss, Endstage kidney disease) scores in 178 patients undergoing open heart surgery at the Clinic of Cardio- vascular Surgery in Târgu Mureș, Romania, between October 1, 2010 and March 31, 2011, and studied the morbidity and mortality in patients with renal dysfunction in terms of these scores. Results: According to AKI criteria, we identified 39 patients having high risk for developing renal injury (stage I) (with 16 cases more than with RIFLE criteria, class R), but we observed no differences in the number of renal dysfunction (28 patients) or renal failure (18 patients). The patients enrolled in high risk group according to AKI score, but not with RIFLE criteria, had a good outcome with diuretics and avoidance of nephrotoxic agents. Two patients needed renal replacement therapy, both of them were classified in the renal failure group. Mortality was higher in renal failure according to both RIFLE and AKI criteria. Conclusions: AKI criteria are more sensitive in identifying patients at risk for renal injury, but the RIFLE criteria are more accurate in the estima- tion of postoperative morbidity and mortality.