We completed a national study of blindness in children under 16. Approximately 80% of the blind children (that is, with vision of 3/60 or less) in the Republic of Ireland (172 children) were seen, 93 males and 79 females. The survey was carried out between July 1989 and June 1990. It is the first such study to be carried out. Ninety seven (56%) children had lesions due to factors acting before the perinatal period. Of these, 28 (16% of the total number surveyed) had lesions due to genetic causes; 69 (40%) had lesions due to factors operating in the prenatal period other than genetic factors. Forty six (27%) had lesions due to factors acting in the perinatal period. Twenty two (13%) had lesions due to factors acting in childhood. (4% could not be categorised in this way). The commonest single primary diagnoses were birth asphyxia in 19 (11%) cases and retinopathy of prematurity in 19 (11%) cases.