In a series of 61 patients with the morphologic and histochemical features of mitochondrial myopathy, 22 (36%) had pigmentary retinopathy. Three patterns of retinopathy were identified. Eighteen patients had a "salt and pepper" type of retinal appearance, which was usually associated with good visual function. Two had many features of retinitis pigmentosa, and two others showed generalized loss, or atrophy, of the retinal pigment epithelium and choriocapillaris. These last four patients had markedly reduced visual acuities, with optic atrophy and attenuated retinal vessels. Electroretinography and electro-oculography were performed in 11 patients. Both rod and cone mediated electroretinographic functions were subnormal in eight patients, while only cone mediated functions were depressed in the remaining three. The electro-oculographic changes were variable.