Background and Purpose — The ability to predict future strokes in asymptomatic patients with carotid stenosis is currently limited. The management of symptomatic patients with <50% stenosis is also debatable. In this context, we performed the following open prospective study to identify factors affecting symptomatology in patients with carotid stenosis. Methods — During 1988–1997, 442 arteries with various degrees of stenosis were followed with the use of color Duplex ultrasonography every 6 months. The main outcome measures were development of symptoms related to the carotid territory and progression in the degree of stenosis. Results of follow-up were analyzed in relation to the traditional risk factors for atherosclerosis as well as the ultrasonographic characteristics of the plaques. Statistical analysis was performed by multiple linear and Cox regression analysis. Results — Mean duration of follow-up was 44 months (range, 12 to 120 months). Significant progression of stenosis occurred in 18.5% of the cases and was more frequent in younger patients ( P =0.09), in patients with coronary artery disease ( P =0.02), and in patients with echolucent plaques ( P =0.02). In regard to clinical presentation, men ( P =0.07), hypertensives ( P =0.07), and patients with echolucent plaques ( P =0.09) showed a trend toward higher frequency of stroke in their history. During the follow-up period, neurological events developed in 12.4% of the cases and were associated with the severity of carotid disease ( P <0.001), history of neurological events ( P =0.02), progression of stenosis ( P =0.002), echolucent plaques ( P =0.01), and hypertension ( P =0.02). Conclusions — Factors other than degree of stenosis and history of neurological events are also important in determining high-risk carotid plaque. In our study hypertension, echolucent plaques, and progressive lesions were associated with an increased risk of neurological events. These factors should be taken into consideration in determining treatment strategies for carotid stenosis.