During follow-up after 34 centers random- ized 1662 patients, the Data and Safety Monitoring Committee called a halt to the trial because of a clear benefit in favor of CEA. Patients randomized to surgery had contrast angiography showing diameter-reducing lesions of 60% using the North American method of measurement. Both treatment groups received what at the time was considered best medical man- agement. The aggregate risk over 5 years for ipsilateral stroke, any perioperative stroke, and death was 5.1% for the surgical patients and 11% for the medical patients (RR reduction, 53%; 95% CI, 22 72). The 30-day stroke morbidity and all-cause mortality for CEA was 2.3%, which included a 1.2% stroke complication rate for catheter angiography. It was suggested that the complications of angiography should be considered part of the risk of surgery because an angiogram would not have been performed if surgery were not contemplated. It should be noted that ACAS was conducted at a time when best medical management was limited to control of BP, the control of diabetes mellitus, and the use of daily aspirin. The value of statins and newer antiplatelet drugs had not been established. The Asymptomatic Carotid Surgery Trial (ACST), carried out primarily in European centers,514 included 3120 patients with asymptomatic carotid stenoses of 70%, as measured by duplex ultrasonography. Subjects were randomized to imme- diate CEA versus indefinite deferral of the operation. The trial used end points that were different from those used in ACAS (perioperative stroke, MI or death, and nonperiopera- tive stroke). The net 5-year risks were 6.4% in the immediate surgery group and 11.8% in the deferred surgery group for any stroke or perioperative death (net gain, 5.4%; 95% CI, 3.0 7.8; P<0.0001). In subgroup analysis, the benefits of CEA were confined to patients <75 years of age. 