Objectives The study objective was to determine the impact of diabetes on radial artery and saphenous vein graft occlusion and clinical outcomes more than 5 years after coronary artery bypass surgery in the multicenter Radial Artery Patency Study (NCT00187356). Methods A total of 529 patients aged less than 80 years with triple-vessel disease undergoing coronary bypass surgery participated in this study. Angiographic follow-up occurred more than 5 years after surgery with annual clinical follow-up. The primary objective was to compare the proportion of complete graft occlusion between radial artery and saphenous vein grafts among diabetic and nondiabetic persons. Additional objectives included determining predictors of complete graft occlusion and comparison of major adverse cardiac events defined by cardiac death, late myocardial infarction, and reintervention. Results There were 148 of 529 patients (27.8%) with diabetes; 269 patients (83/269 30.9% diabetic) underwent late angiography at mean of 7.7 ± 1.5 years after surgery. In diabetic patients, the proportion of complete graft occlusion was significantly lower in the radial grafts (4/83 4.8%) than in the saphenous grafts (21/83 25.3%) ( P  = .0004), and this was similar in nondiabetic patients ( P  = .19). Multivariate modeling showed that the use of the radial artery and high-grade target vessel stenosis were protective against late graft occlusion, whereas female gender, smoking history, and elevated creatinine were associated with an increased risk; interaction between diabetic status and conduit type also was significant ( P  = .02). Major adverse cardiac events were higher in diabetic patients (23/148 15.5% vs 35/381 9.2%, P  = .04). Conclusions The use of the radial artery should be strongly considered in diabetic patients undergoing coronary bypass surgery, especially with high-grade target vessel stenosis.