BACKGROUND AND PURPOSE: The ability of the ivy sign on contrast-enhanced T1-weighted MR imaging (CEMR) to reflect cerebral perfusion and postoperative revascularization in Moyamoya disease remains largely unknown. We aimed to compare the capabilities of CEMR and FLAIR. MATERIALS AND METHODS: CEMR, FLAIR, arterial spin-labeling, and DSA were performed in 44 patients with Moyamoya disease. The ivy sign was scored separately on CEMR and FLAIR using the Alberta Stroke Program Early CT Score. The status of leptomeningeal collaterals was scored on DSA. The postoperative Matsushima grade was evaluated at least 3 months after surgical revascularization. RESULTS: Scoring of the ivy sign on CEMR showed excellent interrater reliability, and FLAIR vascular hyperintensity showed moderate interrater reliability. Correlation analyses revealed that DSA scores were more consistent with the CEMR-based ivy sign score (r ¼ 0.25, P ¼ .03) than with FLAIR vascular hyperintensity (r ¼ 0.05, P ¼ .65). The CEMR-based ivy sign score was significantly correlated with CBF in late-Suzuki stage Moyamoya disease (t ¼ À2.64, P ¼ .02). The CEMR-based ivy sign score at baseline was significantly correlated with the postoperative Matsushima grade (r ¼ 0.48, P ¼ .03). CONCLUSIONS: In this study, CEMR outperformed FLAIR in capturing the ivy sign in Moyamoya disease. In addition, the CEMR-based ivy sign score provided adequate information on hemodynamic status and postoperative neovascularization. The current study suggested that CEMR could be considered as an alternative to FLAIR in future studies investigating leptomeningeal collaterals in Moyamoya disease. ABBREVIATIONS: CEMR ¼ contrast-enhanced T1-weighted MR imaging; FVH ¼ FLAIR vascular hyperintensity; MMD ¼ Moyamoya disease; PCA ¼ posterior cerebral artery; EDAS ¼ encephaloduroarteriosynangiosis; FOV ¼ field of view M oyamoya disease (MMD) is an uncommon cerebrovascular disease characterized by chronic progressive occlusion of the terminal portion of the internal carotid artery and its main branches within the circle of Willis. 1,2 In MMD, the perfusion of brain tissue originates from the narrowed ICA, basal moyamoya vessels, leptomeningeal collaterals derived chiefly from the posterior circulation, and transdural collaterals from the external carotid