Background and aims. It has been largely studied and proven that tight glycemic control is necessary for the favorable outcome of coronary artery bypass graft (CABG) as it is associated with less morbidity and mortality. Insulin is considered as the fastest and safest means to control blood glucose in patients with type 2 diabetes mellitus (T2DM) in perioperative period. The aim of our study was to assess the preoperative risk factors for hyperglycemia after CABG. Material and methods. 70 insulin-naive T2DM patients undergoing CABG were included in the study. Anthropometric, biochemical and hormonal examinations were performed before the operation. Hyperglycemia was managed with insulin. Continuous intravenous insulin infusion was used according to the Portland Protocol until the third postoperative day (target serum glucose concentration <180 mg/dl). Patients were switched to subcutaneous insulin injections using intermediate and fast acting insulin after moving to the ward (Insulatard 100 IU/ml, Actrapid 100 IU/ml, Novo Nordisk A/S) until the day of discharge. All patients had 3—4 times daily capillary blood glucose check in the ward and mean daily glucose value was calculated. Results. The postoperative blood glucose values correlated significantly with the preoperative HbA1c values (p<0.05). The daily dose of insulin required to correct hyperglycemia correlated more with HbA1c values (p<0.005) than with patients’ weight (p<0.05). Conclusion. The preoperative good metabolic control in necessary for the patients awaiting CABG. The value of HbA1c should be considered to estimate the daily dose of insulin.