The RIFLE classification, which defines three grades of increasing severity of acute kidney injury--risk (RIFLE R), injury (RIFLE I) and failure (RIFLE F), and two outcome classes (L, loss) and E (end-stage kidney disease)--represents a valuable method for evaluating acute renal failure. Risk factors for acute kidney injury (AKI) according to the RIFLE criteria and for operative mortality were identified in patients undergoing valvular procedures.A single-center prospective cohort study of 1424 patients who were not receiving renal replacement therapy preoperatively was conducted between January 2004 and December 2007. A total of 100 variables was collected from each patient.The main features were: mean age 61.9 +/- 12.9 years (range: 15-88 years), 47% females, 6% endocarditis, 11% redo surgery, 8% urgent/emergent surgery, 30% combined procedures, 5% complex, and 16% associated coronary artery bypass grafting (CABG). The overall AKI prevalence was 10%, with RIFLE scores of I or F being detected in 8% and continuous veno-venous hemofiltration being required in 5%. Risk factors for AKI were age (OR 1.03; 95% CI 1.14-4.15), time of extracorporeal circulation (ECC) (OR 1.09; 95% CI 1.005-1.013), redo procedure (OR 2.35; 95% CI 1.42-3.8), chronic kidney disease (OR 3.2; 95% CI 1.6-6.1), and blood transfusion (OR 3.8; 95% CI 2.5-6.5). The transfusion of leukodepleted blood exerted a protective effect on AKI development (OR 0.6; 95% CI 0.4-0.9). The average overall hospital mortality was 4.8%. Risk factors for operative mortality included: ECC time (OR 1; 95% CI 1.002-1.014), age (OR 1.043; 95% CI 1.01-1.07), chronic kidney disease (OR 4.8; 95% CI 2.2-10.6), blood transfusion (OR 6.43; 95% CI 2.8-14.7), surgical priority (OR 6.5; 95% CI 2.8-14.7), RIFLE class I (OR 11.9; 95% CI 5.5-25.7), and RIFLE class F (OR 30; 95% CI 8.1-111.7). Mortality increased with each RIFLE stratification (Normal 1.7%, RIFLE R = 4.1%, RR = 2.5; RIFLE I = 27.6%, RR = 16.2; and RIFLE F = 43.8% RR = 25.8).AKI is a highly prevalent and prognostically important complication, for which the majority of risk factors that have been identified are not modifiable. The transfusion of leukodepleted blood products was seen to exert a preventive effect.