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The progression of carotid stenosis may be a better predictor of adverse neurological outcomes than a single measurement of stenosis in asymptomatic patients.Retrospective review of prospectively collected data from a noninvasive vascular surgery laboratory between 1988 and 1997 at a Veterans Affairs Medical Center. A total of 1701 carotid arteries from 1004 asymptomatic patients were prospectively followed by duplex ultrasonographic scanning. Carotid arteries treated with endarterectomy were excluded. The main outcome measures were ipsilateral transient ischemic attack (TIA) and cerebrovascular accident (CVA).The baseline degree of carotid stenosis was less than 50% of artery diameter in 75% of patients. The annual rates of ipsilateral TIA and CVA were each 3.3%. When categorized with respect to carotid artery, the annual rates of ipsilateral TIAs and CVAs were 2.0% and 2.1%, respectively. Univariable Cox proportional hazards modeling showed that both baseline carotid stenosis and progression of stenosis were significant predictors of the composite outcome TIA and CVA, as well as the outcome CVA alone. In multivariable modeling, the progression of carotid stenosis was a highly significant predictor of the composite outcome TIA and CVA (risk ratio [RR], 1.68; P.001) and of CVA alone (RR, 1.78; P.001). However, baseline stenosis was found to be a significant predictor of time to the combined outcome (RR, 1.29; P =.01) but not of CVA alone. Clinical risk factors did not add any additional predictive information.The progression of carotid stenosis assessed by serial duplex scanning is a better predictor of ischemic neurological events than a single measurement of stenosis.