Detailed light and electron microscopic examination of early idiopathic preretinal fibrosis lesions showed that the fibrosis consisted of a layer of glial cells on the retinal surface. Two cases supported the clinical observation that a glinting retinal reflex preceded the development of retinal folds and traction lines. In both cases there was a break in the inner limiting lamina through which glial cells migrated and, presumably, proliferated on the retinal surface. There was no evidence for vitreoretinal adhesions. The ultrastructural similarity of the lesion to preretinal glial membranes seen in other disease entities suggested the possibility of a common biochemical stimulus for glial cell migration and proliferation on the retinal surface.