Moyamoya formations at the base of the brain are not congenital vascular malformations but represent collateral pathways associated with chronic progressive stenosis of the carotid fork. The authors have studied 44 personal cases, 18 children under 15 years of age, and 26 adults. In children the Moyamoya vessels change through six stages: (1) carotid fork stenosis; (2) progressive carotid stenosis with initial Moyamoya collaterals and dilatations of cerebral arteries; (3) dilatation of Moyamoya collaterals and disappearance of anterior and middle cerebral arteries; (4) thinning of Moyamoya; (5) contraction of Moyamoya and disappearance of posterior cerebral arteries; (6) intracerebral vessels perfused from the external carotid and/or vertebrae. These six stages are not observed in adults. Bilateral cervical perivascular sympathectomy (PVS) was performed in 9 children and superior cervical ganglionectomy (SCG) was added unilaterally in 4 and bilaterally in 3 cases. Angiographic follow-up studies were carried out 1-7 years following surgery. Improvement was observed in most of the cases examined within the first 2 months after surgery. This was not the case in arteriograms performed more than 6 months postoperatively. It would seem that PVS and SCG can improve the progress of Moyamoya vessels but only for a short period of time. Clinical symptoms, however, seem to continue improving over a long period of time. Cerebral blood flow improved 5 weeks following surgery in a 13-year-old boy.