Color Doppler US is at present the most reliable noninvasive procedure in the diagnosis of carotid disease and plays a major diagnostic role in the patient at risk for stroke. The anatomofunctional relationships of carotid and vertebrobasilar system suggest a diagnostic combination between Doppler US and transcranial Doppler for complete hemodynamic evaluation of normal and pathologic cerebral vessels. The most relevant disease, as the cause of stroke, is represented by internal carotid atherosclerosis. Mechanisms by which the atheromatous plaque represents a cause of ischemia involve two factors: the embolic factor and the hemodynamic factor. The embolic factor is consequent on unstable plaques and US plays a major role in plaque characterization. Stenotic plaques are the major cause of the hemodynamic factor. Color Doppler US inables quantification of stenosis and selects surgical patients with greater than 70% stenosis. In internal carotid dissection as the acute cause of cerebrovascular insufficiency color Doppler US findings are significant for early diagnosis and follow-up.