Cerebral mycotic angitis takes place as a secondary disease to inflammation which is precipitated on the arterial wall to the artery, most frequently the vasa vasorum, as a result of settlement of infectious embolus into there, and it is usually seen in the patient with cardiac disease. The middle cerebral artery is a major region where the lesion takes place in multitude, and it is only rarely seen in the patient having infection in the brain or dura mater. We have recently experienced a very rare case in which false aneurysm was induced in the internal carotid artery by angitis due to Aspergillus, and this report deals with case. A 26-year-old office-man: He was attacked by loss of consciousness, aphesia, right hemiparesis during work in his office. As left CAG demonstrated evidence of arteriovenous malformation, redical operation was performed. He took a favorable course postoperatively, but developed meningitis on 10th day, when massive antibiotic therapy was started. During treatment, however, his consciousness rapidly decreased, and it was found on left CAG that there was false aneurysm in the cisternal segment of the left internal carotid artery which has previously been completely healthy. Operation was practiced once again to reinforce the wall of the left internal carotid artery, but the patient died of aggravated meningitis. Autopsy demonstrated a very fragile left internal carotidartery associated with perporation which was surrounded byprominent coagula. Histological examinations indicated that the perforation of the vascular wall had been caused by angitis due to Aspergillus infection.