Moyamoya disease is characterized by progressive occlusion of the supraclinoid internal carotid artery and the circle of Willis with the simultaneous appearance of natural intracranial and extracranial collaterals [1]. Initial manifestation of this disease usually occurs as a cerebrovascular event such as cerebral infarction, hemorrhage, transient ischemic attack, and occasionally, epileptic seizure [2]. We report an uncommon case of moyamoya disease presenting with fluctuating frontal lobe dysfunction. A 45-year-old right-handed woman presented with fluctuating confabulation, inappropriate behavior, and mood changes that started 2 weeks prior. She had no medical history of hypertension, diabetes mellitus, angina pectoris, hyperlipidemia, or psychiatric illness. Symptoms had occurred three times over a 2-week period, and each symptom persisted for several hours. Her symptoms occurred under emotionally stressful conditions. On neurological examination, we could not find any focal neurological signs or symptoms except a mild depressive mood. Blood cell counts and other laboratory tests were normal. We initially thought that her problems might originate from her depressive mood. One week later, she presented with transient right-sided weakness in addition to continuation of the previous behavioral symptoms. She reported that the symptoms occurred after a stressful quarrel with her husband. At that time, she showed Medical Research Council grade IV limb weakness. Her transient right-sided weakness resolved completely after 1 h. The diffusion and T2-weighted brain magnetic resonance image (MRI) showed spotty high signal intensity lesions on the left frontal subcortical white matter, suggesting acute cerebral infarction (Fig. 1a). Brain MRI showed no old ischemic lesions. Magnetic resonance and conventional angiography showed severe stenotic and occlusive lesions of the bilateral middle cerebral and distal internal carotid arteries with rete formation, suggesting moyamoya disease. Conventional angiography also revealed transdural anastomosis and numerous posterior collateral vessels (Fig. 1b–f). There were no other definite causes of central nervous system vasculitis. There were negative findings on human immunodeficiency virus and venereal disease research laboratory test. There was no evidence of CSF inflammation. Patient had an erythrocyte sedimentation rate of 10 mm/hr and a C-reactive protein of 0.1 mg/dL. Blood tests including anticardiolipin antibody, lupus anticoagulant, antinuclear antibody and anti-neutrophil cytoplasmic antibody were also unremarkable. Neuropsychological testing showed definite frontal lobe dysfunction. Her Mini Mental State Examination score was 25, and she showed poor performances on the Stroop testcolor reading, the Controlled Oral Word Association Test (COWAT), and motor programming tasks. There was no deficit on copy of Rey-Osterrieth’s figure. All tasks revealed slowness and perseveration, and euphoria and aberrant motor perseveration were found on the neuropsychiatric inventory (NPI). Brain single photon emission computed tomography (SPECT) images taken 4 days after her transient rightsided weakness and behavioral changes displayed a perfusion defect in the left frontal area (Fig. 2a, b). The patient K. O. Lee K.-Y. Lee (&) Department of Neurology, Gangnam Severance Hospital, Yonsei University College of Medicine, 712 Eonjuro, Gangnam-gu, Seoul 135-720, Korea e-mail: kylee@yuhs.ac