Introduction: Iron deficiency is widespread in the developing world and is especially common in young children who live on the Indian subcontinent. Supplementation with iron and folic acid alleviates severe anaemia and enhances neurodevelopment in deficient populations, but little is known about the risks of mortality and morbidity associated with supplementation. Methods: We did a community-based, cluster-randomised, double-masked, placebo-controlled, 2×2 factorial trial in children aged 1-36 months and residing in southern Nepal. We randomly assigned children daily oral supplementation to age 36 months with: iron (12.5 mg) and folic acid (50 μg; n=8337), zinc alone (10 mg), iron, folic acid, and zinc(n=9230), or placebo (n=8683); children aged 1-11 months received half the dose. Our primary outcome measure was all-cause mortality, and our secondary outcome measures included cause-specific mortality and incidence and severity of diarrhoea, dysentery, and acute respiratory illness. Analyses were by intention to treat. This study is registered at clinicaltrials.gov, number NCT00109551. Findings: The iron and folic acid-containing groups of the study were stopped early in November, 2003, on the recommendation of the data and safety monitoring board; mortality in these groups did not differ from placebo and there was low power to detect positive or negative effects by the time enrolment was completed. We continued to enrol children to the placebo and zinc alone groups. 25 490 children participated and analyses are based on 29 097.3 person-years of follow-up. There was no difference in mortality between the groups who took iron and folic acid without or with zinc when compared with placebo (HR 1.03, 95%CI 0.78-1.37, and 1.00, 0.74-1.34, respectively). There were no significant differences in the attack rates for diarrhoea, dysentery, or respiratory infections between groups, although all the relative risks except one indicated modest, non-significant protective effects. Interpretation: Daily supplementation of young children in southern Nepal with iron and folic acid with or without zinc has no effect on their risk of death, but might protect against diarrhoea, dysentery, and acute respiratory illness. Introduction: Iron deficiency is widespread in the developing world and is especially common in young children who live on the Indian subcontinent. Supplementation with iron and folic acid alleviates severe anaemia and enhances neurodevelopment in deficient populations, but little known known the risks of mortality and Methods: We did a community-based, cluster-randomized, double-masked, placebo-controlled, 2 × 2 factorial trial in children aged 1-36 months and residing in southern Nepal. We randomly assigned children daily oral supplementation to age 36 months with iron (12.5 mg) and folic acid (50 μg; n = 8337), zinc alone (10 mg), iron, folic acid and zinc Our primary outcome measure was all-cause mortality, and our secondary outcome measures included cause-specific mortality and incidence and severity of diarrhea, dysentery, and acute respiratory illness. A nalyses were by intention to treat. This study is registered at clinicaltrials.gov, number NCT00109551. Findings: The iron and folic acid-containing groups of the study were stopped early in November, 2003, on the recommendation of the data and safety monitoring board ; mortality in these groups did not differ from placebo and there was low power to detect positive or negative effects by the time enrolment was completed. We continued to enrol children to the placebo and zinc alone groups. 25 490 children participated and analyzes are based on 29 097.3 person-years of follow-up. There was no difference in mortality between the groups who took iron and folic acid without or with zinc when compared with placebo (HR 1.03, 95% CI 0.78-1.37, and 1.00, 0.74-1.34 , respectively). There were no significant differences in the attack rates for diarrhea, dysentery, or respiratory infections between groups, although all the relative holidays except one indicated modest, non-significant protective effect s.Interpretation: Daily supplementation of young children in southern Nepal with iron and folic acid with or without zinc has no effect on their risk of death, but might protect against diarrhea, dysentery, and acute respiratory illness.