One hundred patients had bilateral aphakia, primary rhegmatogenous retinal detachment, and adequate visualization of the retinal and vitreous in the fellow eye. Of 43 patients with posterior vitreous separation and no retinal tear in the fellow eye, only one (2%) subsequently developed retinal detachment. Of 40 patients without posterior vitreous separation in the fellow eye, eight (20%) later developed retinal detachment following posterior vitreous separation. The remaining 17 patients had posterior vitreous separation and retinal tear or detachment at the time of initial examination. Thus, if posterior vitreous separation occurs without forming retinal tear, the risk of developing retinal detachment is significantly lowered.