Three hundred and eighteen of 421 children (76 per cent) registered in Chile's 10 schools for the blind were examined. 84 per cent of these had severe visual loss (severe visual impairment or blindness), which was attributable to hereditary factors in 29.6 per cent, intra-uterine factors in 8.2 per cent, perinatal factors in 22.5 per cent and childhood factors in 11.2 per cent. The aetiology could not be determined in 28.5 per cent. Retinopathy of prematurity (ROP) accounted for 17.6 per cent of all children with severe visual loss; analysis of data by age-group suggested that ROP is becoming an increasingly important cause of blindness. It is estimated that one-half of the children with severe visual loss in Chile have avoidable causes of blindness. The findings are discussed in the light of possible control strategies.