Background. The association between perioperative hyperglycemia and outcomes in patients with and without diabetes mellitus undergoing coronary artery bypass grafting is not well defined. We measured the association between perioperative hyperglycemia and outcomes among patients undergoing coronary artery bypass grafting. Methods. We report a historic cohort study of 1574 patients who had undergone coronary artery bypass grafting between 1998 and 1999, 545 (34.6%) with diabetes. Perioperative blood glucose level was defined as the average of all blood glucose tests obtained on the day of and the day after surgery. Outcomes were 30-day mortality, infection rates (sternum, harvest site, sepsis, pneumonia, urinary tract), and resource utilization. Results. After adjusting for diabetes status and calculated preoperative mortality or mediastinitis risk scores, each 50 mg/dL (2.78 mmol/L) blood glucose increase was not statistically associated with higher mortality (odds ratio 1.37; 95% confidence interval, 0.98 to 1.92; p = 0.07), or higher infection rate (odds ratio 1.23, 95% confidence interval 0.94 to 1.60; p = 0.14). Each 50 mg/dL blood glucose increase was associated with longer postoperative days by 0.76 days (95% confidence interval 0.36 to 1.17 days; p < 0.001), increased hospitalization charges by $2824 (95% confidence interval $1599 to $4049; p < 0.001), and increased hospitalization cost by $1769 (95% confidence interval $928 to $2610; p < 0.001). In the unadjusted analysis, infections occurred more frequently in patients with diabetes (6.6% vs 4.1%, p = 0.03). Conclusions. Perioperative hyperglycemia is associated with increased resource utilization in patients undergoing coronary artery bypass grafting with and without diabetes. © 2003 by The Society of Thoracic Surgeons.