Aim: To investigate whether 3-monthly oral supplementation of 100,000iu vitamin D reduces pneumonia and its consequences among children aged 1-12 months (followed for 18 months), living in a deprived area of Kabul, Afghanistan, where >70% of young children are vitamin D deficient (<8ng/dl). The effect of vitamin D on the incidence of other diseases, in particular diarrhea and rickets will also be investigated.