In dependence on the various statistics, hereditary causes are identified in up to 50% of the visually handicapped and blind school children. Most common are retinal disorders, which account for 15 to 55%. The most important diseases are briefly reviewed: Leber's congenital amaurosis, rod monochromacy, blue cone monochromacy, congenital stationary night blindness (CSNB), X-linked retinitis pigmentosa, Usher syndromes, Bardet-Biedl syndrome, juvenile neuronal ceroid lipofuscinosis Spielmeyer-Vogt, the various forms of albinism, exsudative vitreoretinopathies including Norrie's disease, as well as Stargardt's macular dystrophy, vitelliform macular dystrophy, and hereditary retinoblastoma. In addition to the clinical symptoms, general genetic principles are stressed, such as mode of inheritance, heterogeneity, expressivity, penetrance, age at manifestation, X-chromosomal gene inactivation, and variability. They all have to be taken into account to correctly establish the diagnosis, to identify family members at risk, and to provide adequate genetic counselling. An overview of the actual molecular genetics of the various retinal disorders is also given.