The recent randomized trials, North American Symptomatic Carotid Endarterectomy Trial, European Carotid Surgery Trial, and Asymptomatic Carotid Atherosclerosis Study, have demonstrated the effectiveness of carotid endarterectomy to reduce the incidence of cerebral infarction in patients with symptomatic and asymptomatic high-grade carotid artery stenosis. However, no studies on Japanese patients have been done until now, and recent progress in endovascular stent treatment has been made. The present prospective, multicenter (not randomized) trial, the Japan Carotid Atherosclerosis Study, has started to analyze present practice and propose treatment guidelines for Japanese patients. Here, the protocol and early results of 565 patients registered until the end of January 2004 are presented.