Vitamin D is known to be of physiological importance outside of bone health and calcium homeostasis, and there is mounting evidence that it plays a beneficial role in the prevention and/or treatment of a wide range of diseases.  Vitamin D appears capable of inhibiting pulmonary inflammatory responses while enhancing innate defence mechanisms against respiratory pathogens. Epidemiological studies have shown that low serum 25-hydroxyvitamin D levels are associated with a higher risk of upper and lower respiratory infections in children. This knowledge is particularly relevant and timely, because infants and children appear more susceptible to viral rather than bacterial infections in the face of vitamin D deficiency. The connection between vitamin D, infections and immune function in the paediatric population indicates a possible role for vitamin D supplementation in potential interventions and adjuvant therapies.  The ideal amount of vitamin D intake needed to prevent the adverse health conditions associated with vitamin D insufficiency/deficiency remains unclear. Disagreements on cut-off values for vitamin D sufficiency in the pediatric population likewise complicate interpretation of the recommendations. Furthermore, recommendations for increased sunlight exposure to promote adequate cutaneous vitamin D3 synthesis will need to be balanced with concerns for the risks associated with the increased time spent in the sun exposed to UV radiation. Based on currently available research, however, support for supplementation greater than what prevents the most adverse outcomes (i.e.  Severe rickets) is strongly advocated. Population-based studies showing an association between circulating vitamin D levels and lung function provide strong justification for randomized controlled clinical trials of vitamin D supplementation in patients with respiratory diseases to assess both efficacy and optimal dosage.