Staging of moyamoya disease Suzuki and Takaku classified the stages of moyamoya disease into 6 stages. According to this classification, many patients fall into the stage 3. Fukuyama and Umezu then further divided stage 3 into 3 subdivisions; 3a, 3b and 3c. Stage 1: Narrowing of carotid fork. Stage 2: Initiation of the "moyamoya vessels"; dilatation of the intracerebral main arteries. Stage 3: Intensification of the "moyamoya vessels"; non-filling of the anterior and middle cerebral arteries.           3a: partial non-filling of the anterior and middle cerebral arteries.           3b: partial preservation of the anterior and middle cerebral arteries.           3c: complete lack of the anterior and middle cerebral arteries. Stage 4: Minimization of the "moyamoya vessels"; disappearance of the posterior cerebral artery. Stage 5: Reduction of the "moyamoya vessels"; the main arteries arising from the internal carotid artery disappear. Stage 6: Disappearance of the "moyamoya vessels"; the original moyamoya vessels at the base of the brain is completely missing, and only the collateral circulation from the external carotid artery is seen. Inconveniences of this classification are as follows: many cases belong to stages 3-5, especially to stage 3. There are few cases in stages 1 and 6. Stages of moyamoya disease are not strongly related to clinical symptoms. In stages 1 and 6, there is no moyamoya vessels on cerebral angiography, which are not moyamoya disease by definition. I have a doubt that there is really vascular dilatation in stage 2. Progression of angiographic stages is commonly observed in children, but in adults many patients often remain in the same stages. This classification is too subjective and even for neurosurgeons it is difficult to define the stages in each moyamoya patient precisely.