Fifty-four cases of massive preretinal retraction were studied using indirect stereoscopic ophthalmoscopy and biomicroscopy with a 3-mirror contact lens. Ten cases were studied before and after the development of massive preretinal retraction. Preexisting vitreous hemorrhage was frequent. Extensive syneresis of the posterior vitreous without detachment of its posterior cortical layer was present in all eyes. The most striking vitreous changes were: (1) shrinkage of the posterior vitreous cortex which degenerated but remained adherent to the detached retina; and (2) contraction of the vitreous gel which was bound posteriorly by a dense equatorial membrane. The equatorial and preretinal membranes observed in well-established cases of massive preretinal retraction are described in some detail. The pathogenesis of massive preretinal retraction is discussed.