A 47-year-old man was admitted because of acute lateral medullary syndrome with severe posterior cervical pain. Cerebral angiography was performed three hours after the onset, which demonstrated that two arteries branched separately from the right subclavian artery, ran upward and formed a single right vertebral artery (VA). One of the two arteries showed both stenosis and luminal dilatation. We thought the structure of these arteries was proximal vertebral artery anomaly and diagnosed him as having dissection of the vertebral artery. We consider that the proximal vertebral anomaly may be a risk for spontaneous VA dissection.