The treatment of calcified coronary lesions by percutaneous coronary intervention has been shown to be associated with poor outcomes and an increased rate of complications. However, the impact of coronary calcification in patients undergoing coronary artery bypass grafting (CABG) is unknown. A total of 755 patients presenting with acute coronary syndrome in the Acute Catheterization and Urgent Intervention Triage Strategy trial underwent CABG. Patients were divided into 3 groups according to the presence and extent of coronary calcifications (lesion level: severe, moderate, none to mild) as assessed by an independent angiographic core laboratory. Major ischemic and bleeding outcomes were assessed at 30 days and 1 year. Severe calcification was found in 103 patients (13.6%), moderate calcification in 249 patients (33.0%), and none-to-mild calcification in 403 patients (53.4%). The presence of severe calcification compared with moderate or none to mild was associated with a significantly higher unadjusted rate of death (11.8% vs 3.7% vs 4.5%, p = 0.006), death or myocardial infarction (MI; 31.1% vs 19.7% vs 16.4%, p = 0.006), and major adverse cardiac event (MACE; 32.0% vs 22.6% vs 20.8%, p = 0.059) at 1 year. By multivariate analysis, severe calcification (vs nonsevere calcification) was identified as an independent predictor of 1-year MACE (hazard ratio 1.49, 95% confidence interval 1.01 to 2.21, p = 0.04) and death or MI (hazard ratio 1.77, 95% confidence interval 1.18 to 2.66, p = 0.006). In conclusion, the presence of severe coronary calcification was associated with worse outcomes after CABG, including an increased risk of death. The presence of severe coronary calcification was identified as an independent predictor of MACE and death or MI 1 year after CABG.