The authors present a rare case of adult moyamoya disease in which a patient experienced rapid progression of cerebral infarction after intraventricular hemorrhage (IVH). A healthy 39-year-old woman was admitted to our hospital with sudden headache, a decreased level of consciousness and mild tetraparesis. Initial magnetic resonance imaging revealed small cerebral infarction and IVH. Although the patient underwent conservative therapy including hypervolemia, hemodilution, keeping moderate hypertension and administration of a free radical scavenger, she showed a fulminant clinical course of cerebral infarction. The authors discuss the possible pathophysiology and suggest the treatment for such cases.