BACKGROUND: In patients with coronary artery disease (CAD), atherosclerotic changes of carotid arteries (CA) often coexist with CAD itself. If the degree of carotid atherosclerosis can be estimated, it would be very helpful in the management of patients with CAD. METHODS: CA intima-media thickness (IMT) was evaluate by ultrasonography at 12segments (both proximal, middle, distal common CA, bifurcation, internal and external CA-of the extracranial CA) on the 182 subjects whom underwent coronary angiograms. The subjects were divided into 4 groups according to the severity of CAD; control (C, n=23), single vessel disease (1, n=64), two vessel disease (II, n=44), three vessel disease (III, n=51). RESULTS: The means (+/-SD) of maximal IMT, chosen from the 12 segments, of each group were 1.4+/-0.7mm (C), 2.1+/-1.4mm (I), 2.2+/-1.2mm (II), and 2.9+/-1.7mm (II). The 4 groups showed significant differences between each other. The only conparison to yield unsignificant differences was between group I and group II (p=0.02 for C and I, p=0.001 for C and II, p<0.001 for C and III, p=0.01 for I and III, p=0.04 for II and III). When multivariate analysis was used to assess which major risk factors for CAD (age, male sex, smoking, hypertension, diabetes, cholesterol, triglycerides and CAD groups affected CA IMT), group III and increasing age were the most significant variables (p=0.0001 and 0.0035, respectively). CONCLUSIONS:It is necessary to evaluate the status of the extracranial carotid arterial system with ultrasonography in patients with three vessel CAD even if neurologically symptomless. It becomes especially evident in elderly patients.