To investigate the role of the vitreous in eyes with central retinal vein occlusion, especially in relation to neovascularization and macular edema, we conducted a retrospective chart review of the vitreous condition of 150 patients (150 eyes) with central retinal vein occlusion. Based on fluorescein angiography findings and color photographs, eyes with central retinal vein occlusion were classified as ischemic or nonischemic. In ischemic cases, retinal or optic disc neovascularization, or both, developed in eight (57%) of 14 eyes without complete posterior vitreous detachment at the final examination. The prevalence of neovascularization was significantly higher than in eyes with complete posterior vitreous detachment (0%, 0/43) at the final examination (p < 0.01). In nonischemic cases, the prevalence of no posterior vitreous detachment or partial posterior vitreous detachment with vitreomacular adhesion was significantly higher in eyes with macular edema (76%, 28/37) than in eyes without it (23%, 13/56) at the final examination (p < 0.01). Complete posterior vitreous detachment may protect against retinal or optic disc neovascularization in eyes with severe central retinal vein occlusion. Vitreomacular adhesion may cause persistent macular edema in eyes with mild central retinal vein occlusion.