A few reports in the ophthalmic literature have described choroidal blood outflow through posterior routes. Most of the patients reported were highly myopic; therefore, a correlation between such posterior routes and high myopia has been suspected. The authors examined highly myopic eyes using indocyanine green (ICG) videoangiography and investigated the prevalence and clinical significance of posterior routes in them. The authors examined 255 highly myopic eyes (146 patients) using ICG videoangiography. All had refractive errors greater than -8.25 diopters (D). They also examined a control group consisting of 42 eyes (26 patients) that had refractive errors within ±3 D. Of 255 highly myopic eyes, 61 (23.9%) had choroidal blood outflow through posterior routes. These routes were classified by type of vein according to its penetration site. One drained into the margin of the optic nerve head, and the other penetrated the sclera near the macula. However, only 1 of the 42 eyes (2.4%) in the control group showed choroidal outflow by a posterior route. The prevalence of posterior routes was significantly higher in the highly myopic eyes than in the control group (P Conclusion: Posterior routes of choroidal blood outflow were observed in nearly 25% of highly myopic eyes. These vessels appear to be one of the major routes of posterior choroidal outflow in highly myopic eyes.