Aim: Lower respiratory tract infections including mainly pneumonia represent an important public health problem leading to high mortality and mobidity rates in children aged below five years in developing countries including our country. Vitamin D deficiency has been associated with increased risk of rickets/osteomalacia, various cancers, autoimmune diseases, hyperproliferative skin diseases, cardiovascular system diseases and infectious diseases. Vitamin D has an important role in cellular and humoral immunity and pulmonary functions. Vitamin D deficiency and lower respiratory tract infection are common health problems in children in our country and no clinical study investigating the relationship between these problems has been conducted so far. In this case-control study, we aimed to assess the association between vitamin D level and lower respiratory tract infection in children.