OBJECTIVES--To investigate the importance of vitamin A deficiency as a cause of childhood blindness and severe visual impairment (SVI) in India. DESIGN AND SETTING--Cross sectional survey of children with visual acuity less than 6/60 in the better eye (SVI/blindness), attending 22 schools for the blind in nine states of India. MAIN OUTCOME MEASURE--Proportion of children with blindness or SVI from corneal scarring attributable to vitamin A deficiency. RESULTS--245 of 1318 (18.6%) of children had SVI/blindness attributable to vitamin A deficiency. The proportion of SVI/blindness due to vitamin A deficiency ranged from 7.5% (7/93) in Kerala to 26.7% (27/101) in Madhya Pradesh. In Tamil Nadu, 7.5% (9/120) of children in the capital city blind school had SVI/blindness due to vitamin A deficiency, compared with 30.4% (51/168) in a blind school in a rural area of the same state. CONCLUSION--Overall, vitamin A deficiency is the single most important cause of childhood blindness and SVI in India. There are marked variations by state and also between urban and rural locations.