A previously healthy 35-year-old man suddenly developed vertebrobasilar ischaemia while playing tennis. Cerebral arteriography revealed a dissecting aneurysm of the cervical portion of both vertebral arteries. The neurological deficit and the angiographic features resolved with anticoagulant treatment alone. Only 15 patients with non-traumatic extracranial vertebral artery dissection have been previously reported. It is necessary to recognize the condition very quickly, because the authors consider that anticoagulation is required as an emergency.