Background: As a predictor of atherosclerosis, intima-media thickness (IMT) of common carotid artery (CCA) shows only weak correlation with extent of coronary artery disease (CAD). The purpose of this study was to find out the characteristics of IMT of CCA as reliable and strong predictors of severity of coronary artery atherosclerosis. Methods: We performed the ultrasound of right CCA by using 15 MHz linear array transducer in 385 patients (M:F = 216:169, Mean age= 61.1짹10.2 ) and underwent the coronary angiography in 268 among them. The internal dimension, maximal IMT irrespective of location and morphology (focal or diffuse), and IMT of 6 more randomly selected points in the CCA were measured. We classified the Plaques as type A (low or equal echo density compared with adventitia) and type B (higher echo density than adventitia). Modified Gensini score was calculated as a marker of the extent of CAD and compared with the results of IMT examination. Results: 1.The carotid plaques were detected in 156/268(58%) patients. 119 were type A and 37 were classified to type B. 2. Gensini score was significantly higher in patients with type B plaque (40.6짹23.5) than patients with type A plaque (29.3짹21.7) (p=0.01). 3. Modified Gensini score was correlated with age (r=0.22 p<0.001), mean IMT (r=0.178, p=0.004) and maximal IMT (r=0.299, p< 0.001). 4. After adjusting the age factor, maximal IMT was the sole independent variable reflecting the severity of CAD.(p= 0.001) Conclusion: Maximal IMT with the type of plaque morphology of CCA provides us more reliable information about the severity of CAD than conventional mean IMT