We have evaluated the relationship between carotid atherosclerotic change and periventricular hyper intensity (PVH). PVH was studied in 66 cases with cerebral thrombosis, comparing them with another group of age-matched controls, which consisted of 29 cases with hypertension, diabetes, and hypercholesteremia. MRI (fluid attenuated inversion recovery) and B-mode carotid ultrasonography of each lesion were analyzed. Thrombosis lesions, compatible with neurological manifestation were divided into two types, cerebral cortical type (including centrum semiovale type) and small infarction in the deep subcortical type. PVH was classified into 4 grades, none, rims/caps, patchy and diffuse. Smooth PVH was, adjoining the anterior/posterior angles and the margins of the lateral ventricles, were defined as caps and rims. Irregular PVH areas, confluent with each other, were defined as patchy, while diffuse PVH areas extending below the cortex beyond the level of the corpus callosum were defined as diffuse. Carotid atherosclerosis was evaluated using B-mode carotid ultrasonography. The severity of carotid atherosclerosis was assessed by using two indicators; incidence of carotid atherosclerosis and maximum percentage diameter of the stenosis areas. Patchy and diffuse type PVH was frequent in the thrombosis group. On B-mode carotid ultrasonography, diffuse PVH was prominent in patients with stenotic change and high maximum percentage of stenosis, but none/rims/caps PVH was accompanied by variable B-mode carotid ultrasonographical findings. Six patients had ulcerated plaques and they suffered more frequently with diffuse PVH. Diffuse PVH was more frequent in cases with severe carotid stenosis than in other PVH types. These findings suggested that large vessel atherosclerosis could result in diffuse PVH.