Ninety-six patients with greater than or equal to 50% unilateral vertebral artery (VA) stenosis were followed up for an average of 4.6 years. In 89 patients (93%) at least one VA origin was involved, while the intracranial VA was affected in 3 patients (3%). Seventy-four patients (77%) had greater than or equal to 50% stenosis of at least one internal carotid artery, of whom 52 underwent carotid endarterectomy. None of the patients had definite vertebrobasilar transient ischemic attacks (VB TIA). Nineteen patients (19.8%) experienced non-localizing symptoms possibly compatible with VB TIA, none of whom had a stroke. Twenty-three patients (24%) had strokes. The only two patients (2%) who sustained a brainstem infarction had fatal strokes and both were known to have basilar artery stenosis in addition to their VA stenosis. The observed stroke rate was 8.5 times the expected infarction rate for a normal population. Forty patients died during follow up. The observed 5-year survival rate was 60% compared to 87% in a matched normal population. Eight deaths (20% of all deaths) were caused by stroke and 21 deaths (52.5% of all deaths) were cardiac related. VA stenosis is most frequently located at the VA origin (93%), and is associated with a low incidence of brainstem infarction.