Aim — to analyze the causes of acute kidney injury (AKI) and multiple organ failure (MOF) followed by replacement renal therapy (RRT) after surgery under cardiopulmonary bypass (CPB). Material and methods. Inclusion criteria were AKI and/or MOF followed by RRT or absence of AKI according to RIFLE-2004. There were 3 groups of patients: group 1 — without AKI, group 2 — AKI without RRT, group 3 — AKI followed by RRT. Data are presented as median, lower and upper quartiles. Differences were significant at p<0.05. Results. AKI followed by RRT occurred in 37 (0.97%) out of 3779 patients who underwent surgery under CPB. Liver failure was observed in 20 cases, MOF — in 30 cases. AKI followed by RRT group was characterized by lower preoperative GFR, higher percentage of combined procedures, advanced blood transfusion, greater CPB and aortic cross-clamping time. The main causes of AKI followed by RRT were bleeding, hemolysis, atrial fibrillation and low cardiac output, sympathomimetics administration. RRT courses for AKI stage II—III were started in 1—3 days after surgery. Kidney function recovery was observed in 40.6% of patients. Mortality rate was 59.4%. Conclusion. AKI in patients undergoing cardiac surgery is caused by circulatory ischemia and inflammatory factors. AKI followed by RRT is associated with advanced in-hospital mortality. Preoperative AKI risk stratification, no contrast agents’ administration on the day of surgery, adequate preoperative hydration, adequate oxygenation and/or optimal perfusion pressure during CPB and early RRT are essential.