A 6-year-old boy developed a flaccid hemiplegia and dysarthria following several transient episodes of nausea, vomiting, and ataxia. An anomaly of the dens was discovered, permitting subluxation of C-1 on C-2. A segmental occlusion of the right vertebral artery and an aneurysm of the left vertebral artery were found at the C-2 level, as well as a thromboembolic occlusion of the rostral end of the basilar artery. It appeared that the repeated cervical subluxation produced occlusive, aneurysmal, and embolic vascular disease, and that clinical symptoms were the result of ischemia in the territory perfused by the vertebrobasilar arteries.