-OBJECTIVE: The long-term outcomes of cognitive func-tion in moyamoya disease remain unknown. We aimed to assess 5-year changes in cognitive function in adult moyamoya disease patients and to evaluate the value of the magnetic resonance angiography (MRA) steno-occlusive score to predict cognitive changes. -METHODS: Participants comprised 20 consecutive pa-tients whose cognitive functions had been evaluated using the Frontal Assessment Battery (FAB) and Neurobehavioral Cognitive Status Examination (Cognistat) at baseline and reassessed 5 years later. -RESULTS: The total FAB score and total Cognistat score were lower after 5 years in 9 patients each. The Wilcoxon signed-rank test showed that subscores for conceptuali-zation and comprehension increased, while subscores for mental flexibility, programming, and inhibitory control significantly decreased after 5 years. The right MRA total score and right posterior cerebral artery score were negatively associated with 5-year changes in the total FAB score and total Cognistat score. The right posterior cere-bral artery score was significantly associated with changes in subscores for mental flexibility, programming, sensitivity to interference, and construction.-CONCLUSIONS: Specific cognitive domains can decline over time in patients with adult moyamoya disease. MRA findings might be useful for predicting future declines in cognitive function.