To assess if the proportion of patients with a primary event differs between patients treated with intensive medical management alone compared to CEA, or to CAS, in patients with high grade asymptomatic carotid stenosis. To assess whether intensive medical management differs from CEA and from CAS to maintain the level of cognitive function at 4 years of follow up To assess if there are treatment differences in major stroke, minor stroke, disabling stroke and tissue based stroke at 4 years, using an analytic approach identical to that for the primary aim. To assess if the CEA or CAS versus intensive medical management difference is affected by patient age, sex, severity of carotid stenosis, restenosis, risk factor level and during of the asymptomatic period

Patients with carotid stenosis will undergo either carotid endarterectomy or carotid artery angioplasty. There are 12 follow-up visits spread over four years. Five of the visits include ultrasounds. An MRI is done at the end of year 4. Medications and blood pressure will be checked and questionnaires answered at each visit.