Objective: One of the most frequently studied parameters in terms of outcome estimation in cardiac surgery is HbA1c. Several studies in literature suggest that high HbA1c value increases mortality and morbidity, but there is no relation between them. The primary aim of the present study is to investigate whether HbA1c value in diabetic patients undergoing coronary bypass graft surgery is an independent predictor for post-operative mortality and morbidity, and our secondary goal was to determine independent risk factors that cause mortality and morbidity in the same patient population., Methods: 380 diabetic patients diagnosed with diabetes who underwent coronary surgery with cardiopulmonary bypass in Mersin State hospital between July 2014 to December 2016 after the approval of the Mersin University Faculty of medicine ethics committee were included in this retrospective, observational, and cross-sectional study. Patient demographic and perioperative information were obtained from the electronic information operating system and from anesthesia-intensive care follow-up forms. The HbA1c threshold was accepted as 7%, which was reported to be more appropriate for evaluating high-risk groups., Results: Three hundred and fifty-four patients with complete access to the data were included in the study. The mean age of the patients was 60.8±9.4 years. 37% of the patients (131 patients) were female. The number of patients with HbA1c≥7 was 194 (54,8%) in the entire patient population. In this study, high HbA1c (≥7) values in diabetic patients undergoing isolated coronary bypass graft surgery were not found to be independent predictors of post-operative mortality and morbidity. Mortality was seen in 28 patients (7.9%). Ejection fraction (EF) was found to be an independent predictor factor for pre-operative factors in logistic regression models constructed according to mortality predictors (OR:0.94; 95% CI: 0.90-0.99; p=0.016). Complications were seen in 50 patients (14.1%). In the models formed from the point of view of the complication predicators, only EF was found to be independent predictor (OR:0.95; 95% CI: 0.92-0.98; p=0.004). It was found that HbA1c was not predictive in all models for mortality and complication (p>0.05)., Conclusion: There are reports in the literature that mortality increases 4-fold when HbA1c value is higher than 8.6% in coronary surgery. However, there is a view that HbA1c alone cannot predict mortality in coronary surgery if diabetes associated factors are excluded. In this study, high HbA1c (≥7) values in diabetic patients undergoing isolated coronary bypass graft surgery were not found to be independent predictors of post-operative mortality and morbidity. Pre-operative low ejection fraction was found as an independent risk factor for post-operative mortality and morbidity in the general patient population., Competing Interests: Conflict of Interest: No conflict of interest was declared by the authors.