A 38-year-old man was admitted to our hospital with headache, dysarthria and paraparesis. Brain CT and diffusion MRI disclosed cerebral infarction at bilateral anterior cerebral artery (ACA) territories. His symptoms and signs deteriorated in several days despite intensive antithrombotic therapy, resulting in right hemiparesis, akinetic mutism, memory disturbance, change of personality, urinary incontinence, forced grasping, and starting delay of speech and motion. Cerebral angiography demonstrated occlusion with contrast pooling at the right ACA A2 portion. Stenosis and dilatation were found at left ACA A2 portion. An intimal flap was also demonstrated on serial angiography. This case was diagnosed as cerebral infarction caused by dissection of bilateral ACA. Although no definite primary arteriopathy was demonstrated, bilateral dissection could be occurred simultaneously.