The morphology of atherosclerosis between the carotid and coronary artery systems was studied in 63 patients with ischemic heart disease to determine if there was a correlation with coronary heart disease. The sclerotic lesions of the carotid and coronary artery systems were imaged with ultrasonography and coronary arteriography, respectively, and divided into 4 types. Hemodynamic variables, serum lipid levels, and serum uric acid concentration were not different among the groups, but the serum C-reactive protein (CRP) concentration in patients without significant atheroma in the carotid artery system was lower than the mean concentration of the other 3 groups with carotid atheroma. The morphological stability of carotid arterial plaques correlated well to coronary artery stenosis. Morphologically unstable plaques of the carotid artery predicted unstable forms of coronary obstruction with a sensitivity of 68%, specificity of 85%, predictive power of 72% and a likelihood ratio of 4.5. These results suggest that ultrasonic examination of the carotid artery is useful for predicting the presence or absence of unstable lesions in coronary arteries.