Sixteen cases of spontaneous dissection of the cervical internal carotid artery (6 verified) are described. The mean age was 45 years. The clinical picture varied from simply headache and a bruit to hemiplegia and aphasia. Eleven patients had transient ischemic attacks. Headache, facial pain, a subjective bruit, oculo-sympathetic palsy and transient monocular blindness were present in various combinations in two-thirds of cases and their presence suggested the correct diagnosis. Examples of suspected dissection of the intracranial internal carotid, middle cerebral, posterior cerebral and extracranial vertebral arteries are also presented. Spontaneous dissection is more common than the literature indicates. © 1978, Canadian Neurological Sciences Federation. All rights reserved.