In order to investigate the relationship between carotid plaque morphology and symptoms of cerebral ischemia, a prospective clinicopathological study was performed. Ninety consecutive intact carotid plaques obtained from surgery and 43 carotid plaques from cadavers without symptoms of cerebral ischemia were evaluated. Ulceration and mural thrombus were the only morphologic findings statistically correlated to the presence of hemispheric symptoms (p less than 0.02). Intramural hemorrhage was more common in patients with hemispheric symptoms but this difference was not statistically significant (p = 0.31). Plaque causing high degree stenosis had a higher incidence of intramural hemorrhage (p = 0.04) and ulceration (p less than 0.02). Ulceration of plaque plays a major role in the onset of hemispheric symptoms. The results of our study support the hypothesis that in the majority of the cases, hemispheric symptoms are embolic in nature.