Moyamoya disease (MMD) is a cerebrovascular occlusive disease characterized by progressive stenosis or occlusion at the distal ends of the bilateral internal carotid arteries. Vascular structural changes were previously detected using postmortem specimens. This study investigated 35 specimens of the middle cerebral artery (MCA) from 25 patients undergoing surgical treatment for MMD. Six MCA samples were also obtained from six control subjects. Histological examination showed that MCA specimens from patients with MMD had significantly thinner media and thicker intima than control specimens. In addition, abnormal findings of the internal elastic lamina and eosin-positive deposits in the intima were detected. Medial thinness and intimal hyperplasia occurred in the MCA of patients with MMD.