Posterior circulation in 82 children of "moyamoya" disease are studied. Two aspects of "moyamoya" disease, (ie; occlusive lesion of cerebral vessels and the development of abnormal vascular network as collateral channel,) are also detected in the vertebrobasilar system. Among 82 cases, 49 cases showed the occlusion of posterior cerebral artery at their quadrigeminal segment. Twenty-three showed the more proximal occlusive lesions. Vertebral artery occlusion were found in 3 cases. As the occlusive lesion progresses, abnormal vascular network at the posterior portion of skull base developed. This network consists mainly of thalamogeniculate artery, posterior choroidal artery, and also of other thalamoperforators. Visual field defect as an ischemic symptom of occipital lobe was detected in 9 cases (11%). Superficial temporal artery-middle cerebral artery anastomosis and encephalo-myo-synangiosis (temporal muscle graft), which were not considered to be so effective to the ischemia of the posterior circulation, were shown to exert indirect redistribution effect upon the vertebrobasilar system. However, this effect is such an indirect one that these surgical treatments cannot prevent the occurrence of ischemic stroke in the vertebrobasilar system. For this purpose, omentum transplantation to the occipital lobe may be needed as a method of direct revascularization.