We analyzed the vitreous findings in 62 patients (62 eyes) with major branch retinal vein occlusion to determine whether vitreous examination was useful in predicting the development of retinal or disk neovascularization, or both. In 18 eyes with no or partial posterior vitreous detachment and large areas of capillary nonperfusion (5 disk diameters or more), ten eyes (55.6%) eventually developed neovascularization. Only three of the remaining 44 eyes (6.8%) developed neovascularization. The probability of this development was greater in eyes with no partial posterior vitreous detachment at the initial vitreous examination (P = .0177, Cox's regression analysis), and in those with large areas of nonperfusion (P = .0097, Cox's regression analysis).