Objectives: To examine whether patients in the Asymptomatic Carotid Atherosclerosis Study reported symptoms of cerebral and retinal ischemia promptly to the investigating team. Design: Cohort study within the Asymptomatic Carotid Atherosclerosis Study, a prospective, randomized, multicenter clinical trial, with a median follow-up time of 2.7 years. Setting: Thirty-nine clinical sites across the United States and Canada. Patients: Patients with asymptomatic carotid artery stenosis (≤60% reduction in diameter) who experienced either a transient ischemic attack (TIA) (n=115) or stroke (n=127) during the follow-up period, as verified by an external committee. Main Outcome Measure: Proportion of patients who reported cerebrovascular symptoms to a study nurse or physician within 3 days of occurrence. Results: Thirty-seven patients (32.2%) experiencing TIA and 57 (44.9%) experiencing stroke reported symptoms to the study staff within 3 days of onset. For TIA, there was a statistically significant inverse association between prompt reporting and the amount of time a patient was enrolled in the study before the event occurred (48% with TIA occurring within 6 months vs 9% with TIA after year 3; P=.04). For stroke, there was a statistically significant association between prompt reporting and treatment arm (56% for the surgical vs 38% for the medical group; P=.05). For either TIA or stroke, none of the other factors examined were significantly associated with prompt reporting. Conclusions: Despite extensive education and reinforcement, fewer than 40% of all first events were reported within 3 days and fewer than 25% were reported in less than 24 hours. Frequent outpatient evaluation of high-risk patients and careful review of symptoms is necessary to determine when asymptomatic carotid artery stenosis has become symptomatic to offer appropriate forms of therapy.