A 65-year-old man with Behçet's disease was admitted to our hospital because of an acute left occipital headache and truncal ataxia. He had been treated with prednisolone since the age of 40. MRI showed a hyperintense lesion on T2-weighted images on the left of the medulla oblongata. Left vertebral angiogram showed findings consistent with a dissection at the V4 segment of the artery. After admission, the patient showed marked improvement and was discharged 1 month later without neurological deficits. This is a very rare case of medullary infarction due to vertebral dissecting aneurysm in a patient with Behçet's disease.