Nineteen patients with bilateral internal carotid artery thrombosis were analysed with respect to long term clinical course from first onset to admission. The patients comprised 19.3% of all patients with occlusive cerebral disease treated in past three years at our clinic. In reviewing the symptoms and signs associated with bilateral carotid occlusions and the clinical course, several patterns became evident and in this report the patients are divided into 3 types: Apoplectic type, those who had severe neurological deficit acutely after occlusion, whose angiography showed impaired or absent collateral circulation, and whose CT scan demonstrated bilateral diffuse low density areas; Progressing type, those whose neurological signs and symptoms grew progressively serious, whose angiography showed moderate or adequate retrograde filling with collateral circulation through posterior cerebral arteries and whose CT scan demonstrated low density lesions in the bilateral frontal lobes; TIA . RIND repeated type, those who had transient ischemic attacks or reversible ischemic neurological deficits repeatedly, whose angiography showed good normograde filling of bilateral internal carotid artery with collateral circulation through posterior communicating arteries and whose CT scan demonstrated no abnormal low density areas except findings of brain atrophy.