Light and transmission electron microscopic examinations of two postmortem eyes from an 80-year-old woman with clinically well-documented Best's macular dystrophy disclosed striking abnormalities in the retinal pigment epithelium (RPE), photoreceptors, and sub-RPE area. The RPE cells were flattened, with displacement of the nuclei toward the apex and diffuse deposition of abnormal lipofuscin and pleomorphic melanolipofuscin granules. A PAS-positive, acid-mucopolysaccharide-negative, electron-dense, finely granular material was deposited in the inner segments of the degenerating photoreceptors and the Mueller cells. An abnormal fibrillar material was present underneath and in close association with the RPE cells, just beneath the area of photoreceptor cell loss. The choriocapillaris was normal. Breaks in Bruch's membrane and neovascularization were noted in the foveolar region. There is evidence that the sensory-retinal changes are primary and that the RPE changes are secondary.