Conclusions: This study is the first to demonstrate noninvasive evaluation of the effect of endolymphatic sac decompression (ESD) in Meniere's disease using magnetic resonance imaging (MRI). Objective: To evaluate the effect of ESD for the treatment of Meniere's disease by applying noninvasive intratympanic gadolinium (Gd) perfusion through the eustachian tube and three-dimensional fluid-attenuated inversion MRI (3D-FLAIR MRI). Methods: This was a prospective study. 3D-FLAIR MRI was performed with a 3 Tesla unit 24 h after intratympanic administration of Gd through the eustachian tube in five patients with intractable Meniere's disease before and 3 months after ESD, with a 2-year follow-up on the effect of ESD. Results: Gd was present in the perilymph of the inner ear in all the patients, which clearly displayed the endolymphatic space on 3D-FLAIR MRI with a visible borderline between the perilymph and the endolymph. According to the normal values for the endolymphatic space, four of five patients had a ratio of more than 26% in the cochlea, and three of five patients had a ratio of more than 41% in the vestibule preoperatively. All the patients had a ratio of less than 26% in the cochlea and 41% in the vestibule postoperatively. ESD was effective in reducing the incidence and severity of vertigo attacks with significant improvement in 60% of patients.