450 villages in northern Sumatra were randomly assigned to either participate in a vitamin A supplementation scheme (n=229) or serve for 1 year as a control (n=221). 25 939 preschool children were examined at baseline and again 11 to 13 months later. Capsules containing 200 000 IU vitamin A were distributed to preschool children aged over 1 year by local volunteers 1 to 3 months after baseline enumeration and again 6 months later. Among children aged 12-71 months at baseline, mortality in control villages (75/10 231, 7·3 per 1000) was 49% greater than in those where supplements were given (53/10 919,4·9 per 1000) (p<0·05). The impact of vitamin A supplementation seemed to be greater in boys than in girls. These results support earlier observations linking mild vitamin A deficiency to increased mortality and suggest that supplements given to vitamin A deficient populations may decrease mortality by as much as 34%.