Atherosclerosis involves the medium and large sized arteries and is a segmental form of generalized arteriosclerosis. After validation study showed that B-mode ultrasonographic intima-media thickness(IMT) of the carotid artery correlated well with hitological IMT, the IMT of the carotid artery has been used as a non-invasive markers of atherosclerosis and even as a surrogate end point of the therapeutic trials. Two methods of measurement are used, one is measuring at multiple extracranial carotid sites in both near and far walls and the other is by computerized measurement at far wall of the distal common carotid artery. We still need a standardization of method of IMT measurement. A large volume of study have shown that there are strong correlations between various cardiovascular risk factors such as age, hypertension, diabetes, smoking, hyperlipidemia, hyperhomocysteinemia, and carotid IMT. Since an autopy study had revealed a strong correlation between cerebral and coronary atherosclerosis, a clinical trial showed that carotid wall thickness by ultrasonography was greater in the patients with coronary stenosis than those with normal coronary angiogram. A recent epidemiological study showed that increased IMT(1mm) represents a high risk of myocardial infarction and/or cerebrovascular disease. Recenly, therapeutic trials have shown that certain lipid lowering drugs and some antihypertensive drugs may have a beneficial effect on IMT progression in asymptomatic or in coronary patients. Thus, carotid IMT by ultrasonography can be used for the early diagnosis of atherosclerosis and for risk stratification of the high risk patient and as an endpoint for therapeutic trials.