Purpose: We sought to assess differences in coronary artery stenosis and coronary atherosclerotic plaques as detected by coronary computed tomography between patients with and without diabetes mellitus according to pretest probability. Methods: We compared coronary artery stenosis and coronary atherosclerotic plaques between 1056 diabetic and non-diabetic patients (334 diabetics) who underwent coronary 64-slice CT for evaluation of suspicious coronary artery disease stratified by pretest probability. Coronary atherosclerotic plaques were classified as calcified (CP), noncalcified (NCP), and mixed plaques (MP). Results: High, intermediate, low, and very low pretest probability were 38, 532, 414, and 72 respectively (mean age: 61.6짹7.3, 58.5짹10.8, 57.5짹10.7, and 49.3짹7.8, male: 63%, 52%, 63%, and 7%, respectively). Patients with diabetes had a higher prevalence of significant coronary artery disease and a higher number of significant-stenosis vessel in intermediate, low, and very low pretest probability groups as compared to controls (patient with significant stenosis: 30% vs. 18%, 30% vs. 12%, and 17% vs. 0%, respectively). Patients with diabetes had a higher prevalence and higher extent of any plaque and MP in intermediate, low, and very low probability groups, of NCP only in low probability group, and of CP in intermediate and low probability groups as compared to controls (p<0.05). Conclusions: In diabetes, computed tomographic angiography can be indicated and useful to detect coronary artery disease and evaluate atherosclerotic plaques in patients with intermediate, low, and very low pretest probability of coronary artery disease.