Background: Pneumonia is the leading cause of childhood mortality, accounting for 19% of the 10.6 million deaths that occur each year1. Case-control studies from Ethiopia2 and India3 suggest that sub-clinical vitamin D deficiency may increase ten times the risk of pneumonia in children. We postulate that controlling childhood vitamin D deficiency has the potential to dramatically reduce the incidence of pneumonia and save >700,000 lives each year since vitamin D deficiency is widespread in developing countries.