We undertook a randomized controlled trial designed to compare the effects of carotid endarterectomy with medical treatment using low-dose aspirin in patients with asymptomatic carotid stenosis. During 30 months of recruitment, 71 randomized and 87 eligible nonrandomized patients participated in a follow-up protocol. The total ipsilateral perioperative stroke and death rate was 0% among randomized patients and 3% among nonrandomized patients, and the major stroke and death rate was 0% for both groups. Too few cerebral ischemic events occurred to judge the comparative effectiveness of carotid endarterectomy versus low-dose aspirin for asymptomatic carotid stenosis. The trial was terminated early because of a significantly higher number of myocardial infarctions and transient cerebral ischemic events in the surgical group than in the medical group. Most of the events were not temporally related to the surgical procedure, but there was evidence that these events could have related to the absence of aspirin use in the surgical group. These observations reinforce the appropriateness of the use of aspirin throughout the perioperative period and beyond (unless contraindications exist) in patients with asymptomatic carotid stenosis who undergo carotid endarterectomy.