Pupils attending 12 schools for the blind in Malawi, 3 schools in Kenya and 2 schools in Uganda were examined to determine the causes of severe visual impairment or blindness (visual acuity in the better eye of less than 6/60). A total of 491 pupils aged 3-22 years was examined. Visual acuity was measured in each eye using a Snellen E chart. The anatomical site of abnormality and underlying cause of visual loss were determined by clinical examination for each eye, and for the child. Information was recorded on a standard reporting form (the WHO/PBL Eye Examination Record for Children with Blindness and Low Vision). Data were analysed for those aged less than 16 years using a database which accompanies the form. Preventable and treatable causes were identified. 260 pupils aged 5-20 years were examined in Malawi, 163 pupils aged 3-19 years were examined in Kenya and 68 pupils aged 6-22 years were examined in Uganda. Of the 491 students included in the study 309 (62.9%) were blind (BL) and 69 (14.1%) were severely visually impaired (SVI). 244 were aged less than 16 years and had SVI/BL. In these 244 children 35.2% of visual loss was due to corneal pathology, 13.5% was due to cataract and 14.8% to diseases of the retina. Corneal pathology, attributed to vitamin A deficiency and measles infection in the majority, was responsible for proportionally more SVI/BL in students in Malawi than in Uganda or Kenya.(ABSTRACT TRUNCATED AT 250 WORDS)