PURPOSE. To identify the risk factors for development of myopic choroidal neovascularization (mCNV), a major cause of visual impairment. METHODS. Enrolled in the study were 23 consecutive patients with bilateral high myopia (axial length, > or =26.5 mm or refractive error, < or =8 D) and unilateral newly developed mCNV who presented to the Myopia Clinic, Osaka University Hospital. Spectral-domain optical coherence tomography (SD-OCT) showed that the fellow eyes had a normal macula. The parameters in the affected and fellow eyes were compared between the individual patients, including best-corrected visual acuity (BCVA), intraocular pressure (IOP), refractive error, axial length, choroidal thickness (CT) (subfoveal, 1.5 mm superiorly and inferiorly), posterior staphyloma height 3 mm from the fovea, length of retinal pigment epithelium (RPE) curvature within 6 mm measured on SD-OCT images, and choroidal degeneration and lacquer crack formation, graded according to a publishedRESULTS. The IOP, axial length, refractive error, and chorioretinal degeneration did not differ significantly. Affected eyes had a significantly higher lacquer crack grade (P < 0.05). The superior CT was not significantly different; the subfoveal and inferior CTs were significantly lower in the affected eyes (P < 0.05 and P < 0.001, respectively). The absolute value of the nasal posterior staphyloma height from the fovea was significantly greater in the affected eyes (P < 0.05), and the affected eyes had a significantly (P < 0.05) longer RPE curvature. CONCLUSIONS. Choroidal thinning resulting from increased RPE/choroid curvature is a risk factor for unilateral mCNV.