Purpose: Cardiovascular events are high in diabetic patients. Even after a normal stress test results, elevated cardiovascular event rates are still observed in diabetic patients compared with non-diabetic patients, which may be mediated through advanced coronary atherosclerosis. We evaluated the difference in the presence, extent, and composition of coronary artery disease (CAD) in patients with and without diabetes using multidetector computed tomography (MDCT). Methods: We studied 315 diabetic patients (47% males and aged 64.6짹11.1 years) and 1497 non-diabetic patients (44.6% males and aged 60.7짹12.5 years) with known or suspected CAD undergoing 64-slice MDCT. The patients had no prior history of revascularization. Coronary arteries without plaque were considered normal. The severity and extent of CAD, plaque of coronary arteries, clinical and laboratory parameters were analyzed. Results: Patients with diabetes had a higher incidence of CAD (72.5% vs 45.9%, p=0000) and a significantly higher obstructive CAD (>50% luminal stenosis) (38.9% vs 18.2%, p=0.000). Among with CAD, diabetic patients had a significantly higher extent of any plaque and mixed plaque, more severe CAD (>70% luminal stenosis(41.9% vs 28.4%, p=0.000). Univariate analysis showed diabetes is significantly correlated with age(odds ratio (OR) 1.03, p=0.000), extent of any plaque(OR 1.22, p=0.000), non-calcified (OR 1.26,p=0.000), mixed (OR 1.34, p=0.000), calcified plaque (OR 1.22, p=0.000) and present (OR 3.11, p=0.000) and obstructive CAD (OR 2.05. p=0.000). On multivariate analysis, the patients with diabetes had higher risk of atherosclerotic CAD and extent of mixed plaque independent of age (OR 1.98, p=0.001 and OR 1.14, p=0.011). Conclusions: In our study, the patients with diabetes had higher frequency of CAD and higher significant stenosis and extent of CAD.