Objectives: We evaluated the clinical significance and identified the predictors of the universal definition of perioperative bleeding (UDPB) classes in patients undergoing isolated coronary artery bypass grafting (CABG). Methods: Data on antithrombotic medication, perioperative bleeding, blood transfusion, and adverse events were available for 2764 patients who had undergone isolated CABG. Results: The Papworth risk score correlated significantly with the UDPB classes (rate of UDPB class 3-4 and Papworth risk score of 0, 12.1%; 1, 23.9%; 2, 37.5%; and 3, 45.0%; P < .0001). Ordinal regression showed that increased age, female sex, low body mass index, low estimated glomerular filtration rate, low hemoglobin, dialysis, urgent or emergency operation, critical status, on-pump surgery, potent antiplatelet drug pause of < 5 days, and warfarin pause of <2 days were independent predictors of high UDPB classes. These risk factors also predicted UDPB classes 3-4 in logistic regression analysis. Increasing UDPB classes were associated with an increased risk of in-hospital mortality (P = .002), stroke (P = .023), low cardiac output (P <. 0001), prolonged use of inotropes (P < .0001), renal replacement therapy (P < .0001), length of stay in the intensive care unit (P < .0001), and late mortality (P < .0001) as assessed by multilevel propensity score-adjusted analysis. Similar findings were observed in the propensity score-adjusted analysis for the most severe grades of perioperative bleeding (ie, UDPB class 3-4). Conclusions: High UDPB classes were associated with significantly poorer immediate and late outcomes. The UDPB classification seems to be a valuable research tool to estimate the severity of bleeding and its prognostic impact affect after coronary surgery.