Afghanistan has one of the highest infant mortalities in the world, and pneumonia is one of the main killers. Moreover, Dietary intake of vitamin D is low and exposure to sunlight is limited due to widespread use of Burqa by women. Two studies in Ethiopia and India suggest that vitamin D deficiency may substantially increase the risk of severe pneumonia among children under-5. Thus a randomized controlled trial was conducted to assess effects ofvitamin Don the incidence of pneumonia. The study was conducted on 3046 children aged 1-11 months (approximately 1500 per arm), in Kabul, Afghanistan. Intervention group was given quarterly 100.000 IU vitamin D (6 doses in total), and control arm received placebo (olive oil). Active and passive surveillance of pneumonia was done for 18 months. Time to the first episode in the Vitamin D group was compared to that in the placebo group using log rank tests and proportional hazards models. The incidence rate ratio for the episodes of pneumonia was calculated using Cox proportional hazard models. Vitamin D had no effect on the incidence of first or only episode of x-ray confirmed pneumonia (RR= 1.06, 95% CI: 0.89- 1.27; p=0.47). The incidence of repeat episodes of xray confirmed pneumonia was higher in the vitamin D group (RR=1.68; 95% CI: 1.28 - 2.21; p <0.00 1 ). Infants 6-12 months old had a higher incidence of pneumonia compared to those <6 months old (RR=2.01; 95% CI: 1.12- 3.63). Children of fathers without any formal education had a higher incidence of repeat episodes of pneumonia compared to children of fathers having any formal education (RR=1.67, 95% CI: 1.20- 2.29). Vitamin D supplementation is not useful to reduce the incidence of pneumonia in children. The effective implementation of measles, OPT, Hib, and pneumococcal vaccines, and IMCI guidelines remain the key strategy to reduce the burden of pneumonia in Afghanistan.