Cerebral angiograms of 34 patients with childhood moyamoya disease have been analysed, this analysis having revealed the following findings. The blood flow to abnormal net-like vessels (ANV) in the base of the brain is mainly supplied from the internal carotid artery (ICA) in the early stage of this disease. In a later stage, however, the blood supply is mainly from the posterior cerebral artery (PCA). Though, no remarkable change was found in the volumes of ANV from the early to later stages of the disease, the leptomeningeal collaterals, the most prominent anastomoses in moyamoya disease, had a tendency to decrease during the later stage with the development of PCA stenosis. Eighteen occlusive PCA lesions were found in the proximal portion of the PCA in eight cases (44%), and in the distal in nine cases (50%). The incidence of aneurysm (1.5%) and intracranial bleeding was low as compared to cases of adult moyamoya disease.