In recent years, there has been a worldwide increase in the incidence of allergy, particularly in the paediatric population. The most common allergic conditions include asthma, allergic rhinitis, allergic conjunctivitis, atopic dermatitis, food allergies and urticaria. There are a number of publications showing the importance of serum vitamin D levels in atopic diseases. The effects of vitamin D on the balance between Th1 and Th2 lymphocyte-mediated immune response as well as the antiinflammatory effects by limiting TNF-α overproduction are emphasised. The role of vitamin D in the formation of natural endogenous antibiotics and antimicrobials, such as defensins and cathelicidins, is also known. Aim of the study: The aim of the study was to assess serum vitamin D levels in allergic children. Material and methods: Children diagnosed with allergy and/or monitored for atopic disease as well as children with recurrent respiratory infections were included in the study. The children were diagnosed and treated at the Department of Paediatrics, Paediatric Nephrology and Allergology of the Military Institute of Medicine in the period from September 2011 to August 2013. A total of 60 children were qualified to a group with allergy diagnosis (group I), and 49 children formed a group with recurrent respiratory infections (group II). Vitamin D levels were measured in 109 children aged from 2 months to 18 years. Results: Low levels of vitamin D (below the normal limit) were shown in both paediatric groups. No statistically significant (p = 0.25) effects of the season on vitamin D levels were found in the whole evaluated population of children. A statistically significant (p < 0.0001) negative correlation was shown between vitamin D serum levels and the age of the assessed children (vitamin D levels decreased with age).