Proper therapy for patients with internal carotid artery stenosis requires a precise pathophysiologic diagnosis that includes characterization and localization of ischemic disease of the brain and knowledge of the arterial disease and the collateral cerebral circulation. Noninvasive techniques such as duplex ultrasound and transcranial Doppler, magnetic resonance angiography, and CT angiography allow precise determination of the stroke subtype and parent arterial pathology. Antiplatelet agents prevent the formation of thrombus on carotid artery atherosclerotic plaque. 3-Hydroxy-3-methyglutaryl coenzyme A reductase inhibitors may help stabilize carotid plaques by altering the plaque morphology and reducing inflammation. Carotid endarterectomy, which is the only procedure proven to be beneficial for patients with asymptomatic disease, should be considered primary intervention. Until ongoing trials for interventional procedures are completed, carotid artery angioplasty and stenting should be considered only in patients with contraindications to carotid endarterectomy. It can be argued that an ideal clinical trial in a high-risk population has not yet been completed. This factor has become even more important with the development of stenting procedures. We have long advocated a trial of only treating patients with hemodynamically significant stenotic lesions (70% to 99%).