Spontaneous dissecting aneurysms of the internal carotid artery occur almost exclusively in the extracranial segment of the artery. The incidence is higher among males and the average age is relatively low (mean: 45 years). The existence of a lesion involving the wall of the carotid artery must be considered in the patient presenting with atypical facial neuralgia or incomplete but painful Horner's syndrome which may or may not be associated with a controlateral neurological deficit. Spontaneous dissecting aneurysms of the internal carotid artery cannot be diagnosed on the basis of a single angiogram. Definite diagnosis requires repeated ultrasonography and/or angiography. Spontaneous recanalization justifies the use of medical therapy (anticoagulant or antiplatelet aggregation therapy) in preference to surgical intervention.