A 2-year-old boy with moyamoya disease that started with neonatal convulsion was presented. Reports of moyamoya disease in infancy are rare. Moyamoya disease was suspected from clinical, neuroradiological, and EEG findings. Cerebral angiography confirmed this diagnosis as stenosis of both carotid siphons and a marked collateral circulation network in perforating arteries. An increase in immunoglobulin to cytomegalovirus was found in his serum, and cytomegalovirus DNA was detected by the PCR method in his blood and cerebrospinal fluid, which suggested a congenital or perinatal infection by cytomegalovirus. This may imply that some viral infections, such as CMV, are involved in the pathogenesis of moyamoya disease. It was also noted that our case was complicated by renal hypertension, which resolved in 4 months. The incidence of renal hypertension by stenosis in the renal artery is about 2%. The renal hypertension is usually permanent. This is the first report of transient renal hypertension associated with moyamoya disease.