Carotid ultrasound is used to noninvasively assess the structure of the carotid wall as well as flow velocity of the common carotid, internal carotid, and vertebral arteries. The intima-media thickness and carotid plaque evaluated by carotid ultrasound enables us to assess the degree of patients' atherosclerotic change. They have been reported to be closely associated with atherosclerotic risk factors and future cardiovascular events. Furthermore, carotid ultrasound allows us to evaluate large artery atherosclerosis and its flow velocity, which provides information on the cause of acute ischemic stroke. Regarding the comparison of ultrasound findings of carotid plaque with its pathology, plaque with calcification shows the highest echogenicity, with fibrous carotid plaque showing the second highest. On the other hand, atheromatous plaque and that with hemorrhage in it show the lowest echogenicity, indicating the vulnerability of plaques. Furthermore, carotid plaque with ulceration or mobility leads to the occurrence of ischemic stroke.