OBJECTIVE The role of the vitreous in eyes with CRVO and its relationship to neovascularization and macular edema, in particular, were investigated. METHODS A retrospective chart review of the vitreous condition of 136 patients (136 eyes) with CRVO was performed. Based on fluorescein angiography findings and color photographs, eyes with CRVO were classified as either ischemic or nonischemic. RESULTS In ischemic cases, retinal or optic disc neovascularization or both developed in 8 (57%) of 14 eyes with no or partial posterior vitreous detachment (PVD) at the final examination. The prevalence of neovascularization was significantly higher than in eyes with complete PVD (0%, 0 of 38) at the final examination (P < 0.01). No significant relationship was found between iris neovascularization development and the vitreous condition or between the prevalence of PVD and macular edema. In nonischemic eyes, the prevalence of no PVD or partial PVD with vitreomacular attachment was significantly higher in those with macular edema (76%, 25 of 33) than in eyes without (25%, 13 of 51) at the final examination (P < 0.01). CONCLUSIONS Complete PVD may protect against retinal or optic disc neovascularization in eyes with severe CRVO. Vitreomacular attachment may cause persistent macular edema in eyes with mild CRVO.