Seven cases of spontaneous occlusion of the internal carotid artery, studied by angiography, are reported. All were males. The course was progressive in 4 and episodic in 3. Associated peripheral or cardiovascular disease was demonstrable in 4 patients. The occlusion occurred in the neck in 5 cases and intracranially in 2. Pneumoencephal-ography disclosed dilated ventricles and/or widened subarachnoid spaces in 6. Electroencephalography revealed slowing of alpha, amplitude asymmetry and diffuse delta activity with focal accentuation in 5. The literature is reviewed. There is no effective treatment.