Background: Moyamoya disease is an idiopathic progressive cerebrovascular steno-occlusive disorder characterized by the formation of numerous collaterals called moyamoya vessels. Accurate evaluation of vascular status and CBF is needed for prompt treatment to prevent ischemic and/or hemorrhagic events. The pathogenesis of the ivy sign on fluid attenuated inversion recovery (FLAIR) images of moyamoya disease patients is unclear. We report a moyamoya disease case wherein the ivy sign changed in relation to SPECT-measured CBF during progression and following treatment. Case Description: A 49-year-old female presented with slight aphasia and right hemiparesis. MRI diffusion-weighted image revealed cerebral infarction in the left frontal lobe. Cerebral angiography images showed bilateral distal internal carotid artery stenosis and moyamoya vessels. FLAIR images exhibited the ivy sign. We performed superficial temporal artery–middle cerebral artery(STA-MCA) bypass surgery with encephalogaleosynangiosis(EGS) and encephalomyosynangiosis(EMS) on the left side 6 months after first presentation. After operation, left-side resting CBF gradually improved on SPECT and the ivy sign decreased. On the other hand, right-side CBF gradually deteriorated at rest, and the ivy sign increased. Therefore, we performed STA−MCA bypass with EGS and EMS on the right side 4 years after first presentation. After operation, resting CBF increased and ivy sign decreased. Conclusion: The FLAIR ivy sign may be a useful indicator of both deterioration and improvement of CBF status without the need for CBF imaging using contrast material.