PURPOSE: The aim of this study was to assess the relationship between serum 25-hydroxyvitamin D3 levels and the severity of atopic dermatitis (AD), markers of atopy (total IgE, total eosinophil count, and eosinophil cationic protein) in AD children according to allergen sensitization. METHODS: This cross-sectional study was carried out on 160 AD patients aged 1 to 18 years between March 2012 and August 2014. The AD patients (AD group) were subdivided into 2 categories according to the results of the allergic skin prick and Unicap tests: the allergic and nonallergic AD groups. We compared 25-hydroxyvitamin D3 levels between the AD and control groups. We also investigated relationships between serum 25-hydroxyvitamin D3 levels, the severity of AD, and markers of AD (total IgE, total eosinophil count, and eosinophil cationic protein) in the allergic and nonallergic AD groups. RESULTS: The average 25-hydroxyvitamin D3 levels were 30.6+/-11.7 and 23.7+/-10.0 ng/mL, respectively, in the control and AD groups (P<0.001). The average 25-hydroxyvitamin D3 levels were 19.7+/-8.6 and 27.5+/-9.8 ng/mL, respectively, in the allergic and nonallergic AD groups, with clinical implications (P<0.001). The 25-hydroxyvitamin D3 levels were not significantly associated with SCORing Atopic Dermatitis index in the allergic (P=0.004, r=-0.092) or nonallergic (P=0.610, r=-0.58) AD groups. The 25-hydroxyvitamin D3 levels were not significantly associated with the aforementioned markers of atopy in the AD group. CONCLUSION: These results suggest that 25-hydroxyvitamin D3 may play a role in the pathogenesis of AD.