Objectives: 25(OH) vitamin D receptors have been describedin immune system cells, particularly those producingantibodies, such as T and B lymphocytes, macrophagesand dendritic cells. This study aimed to investigateserum 25(OH) vitamin D levels in children hospitalizedwith pneumonia.Materials and methods: Eighty patients, 40 male and40 female, aged between 1 and 15 months and hospitalizedwith a diagnosis of pneumonia were included. Fortyhealthy children, 19 female and 21 male, comprised thecontrol group. Patient and control groups were comparedin terms of serum 25(OH) vitamin D, calcium, alkalinephosphatase, parathyroid hormone and CD4/CD8 ratioand bone mineral densitometry. Patients’ fever, coughing,pulmonary auscultation findings, time to amelioration ofradiological appearances and duration of treatment werealso compared.Results: 25(OH) vitamin D levels were below 20 ng/mL in54.7% (n=43) of the patient group and 25% (n=10) of thecontrols (p<0.001). Fever began improving in 2.5 days inthe cases with low serum 25(OH) vitamin D levels, coughingin 5.3 days, pulmonary auscultation findings in 8.4days and radiological findings in 20.6 days. Average timeto healing in cases with serum 25(OH) vitamin D levels<20 ng/mL was 13.7 days, compared to 7.2 days in caseswith serum 25(OH) vitamin D levels >20 ng/mL.Conclusions: Low 25(OH) vitamin D levels may be a riskfactor for childhood pneumonias. Serum 25(OH) vitaminD levels should be investigated in cases of lower respiratorytract infection. We think that if Serum 25(OH) vitaminlevels <20 ng/mL supplemental 25(OH) vitamin D shouldbe given.Key words: Vitamin D, pneumonia, immune system