Background and Purpose-Transcranial Doppler may be used to detect spontaneous cerebral emboli (SCE), but this information will only identify at-risk patients if these individuals are consistently identified over time. We investigated the consistency of SCE production in patients with symptomatic carotid disease. Methods-Transcranial Doppler signals from the ipsilateral middle cerebral artery in 25 patients with symptomatic carotid stenosis of Ͼ70% were recorded over 1 hour for blind analysis by a panel of trained observers. This was repeated at the same time of day, weekly, for 6 weeks. Results-The number of patients with SCE increased with each week of monitoring until 13 (52%) were positive. The range of the cumulative number of SCE was 1 to 6. Ten (40%) patients were positive for SCE during only 1 monitoring session, and 2 (8%) were positive for SCE during 2 sessions. SCE-positive patients tended to have more recent symptoms. The correlation coefficients between time elapsed since last cerebral symptom and SCE were weak and not significant. Conclusions-Most, if not all, patients with severe carotid disease will eventually produce SCE. However, the production of an SCE is random, and it is likely that many hours of monitoring are required to determine whether a patient with symptomatic carotid disease is SCE positive. SCE are unlikely to identify at-risk patients but may indicate periods of transiently increased risk in individual patients. (Stroke. 2002;33:685-688.)