The natural history of patients suffering from bilateral internal carotid occlusion is poorly known. We report a study of 19 patients presenting such a vascular condition as demonstrated by angiography. In all our cases, cardio-vascular risk factors were frequently found. Smoking was particularly frequent and present in 18 patients (95%). Presenting neurological episodes included either transient ischemic attack (8/19) or stroke (9/19). Associated arterial lesions were diffusely distributed on the other cerebral vessels, frequently involving the extra-cranial part of the vertebral arteries. Collateral circulation feeding the intracranial carotid system mainly, or exclusively, originated from the vertebro-basilar system. Ischemic strokes were frequently detected by cerebral CT scan. They were located in the middle cerebral territory or at the junctions between 2 major cerebral arteries. A radiological aspect of cortical atrophy was noted in 9 patients among 19. Regional cerebral blood flow assessed by Xe133 inhalation was usually normal at rest (16/19), but hyporeactivity to acetazolamide was found in 10 patients among 19. The latter was more frequent in patients suffering from arterial hypertension or diabetes mellitus. Our results confirm that the patients suffering atheromatous bilateral occlusion of the internal carotid arteries may survive with minimal neurological deficits. Collateral circulation is mainly provided by the vertebro-basilar system allowing to frequently maintain normal cerebral blood flow at rest.