The commonest cause of blindness among the 67 patients at the Yamanashi School for the Blind was congenital cataract (16). Next was retinitis pigmentosa or choroido-retinal degeneration (8), then retinopathy of prematurity (7). Congenital glaucoma and brain tumor each contributed five. Four were due to microphthalmia/micro-cornea and five to high myopia. Direct ocular trauma caused three. Two each were attributable to complete albinism, aniridia, congenital nystagmus and bilateral retinoblastoma. Single cases each of anophthalmos, Behçet's disease, Hallerman-Streiff syndrome, hydrocephalus, macular degeneration and optic atrophy were recorded. 41.8% of all cases were "very probably" hereditary and a further 10.4% "probably" so. 12.2% of the hereditary cases had consanguineous parents. An autosomal recessive (AR) cause is the likeliest explanation for the majority of the nonenvironmental causes (42.9% very probably AR and 14.3% probably AR), so that the possibility of prevention by genetic counseling was limited, but should have been given as soon as the first affected child was born. Parental consanguinity supports an autosomal recessive cause. 10.2% are very definitely due to an autosomal dominant gene; in them, counseling may well also have had a limited effect but might have prevented the birth of one or both of the siblings with aniridia inherited from the mother, and at least two, if not all three, of the three siblings with congenital cataract also inherited from the mother.