BACKGROUND: Vitamin D metabolism has been associated with type 1 diabetes. OBJECTIVE: We aimed to clarify the association of 25-hydroxylase (CYP2R1) and 1α-hydroxylase (CYP27B1) with risk of developing type 1 diabetes in Korean children. METHODS: In total, 252 children (96 type 1 diabetes and 156 healthy controls) under the age of 20 years were recruited. Serum 25-hydroxyvitamin D (25OHD) and 1α,25-dihydroxyvitamin D [1α,25(OH) D] levels were determined. Allelic, genotypic, and haplotypic distribution of CYP2R1 (rs12794714, rs10766196, rs10741657, rs2060793, and rs10766197) and CYP27B1 (rs4646536, rs10877012, and rs3782130) polymorphisms were determined. Clinical and biochemical data were analyzed according to genotype. RESULTS: Mean vitamin D level was considerably lower, and vitamin D deficiency was more prevalent in children with type 1 diabetes than in healthy controls. The GG genotype of CYP2R1 rs12794714 and AA genotype of CYP2R1 rs10766196 were significantly associated with risk of developing type 1 diabetes (odds ratio 2.00, 95% confidence interval 1.176-3.413 and odds ratio 1.88, 95% confidence interval 1.103-3.195, respectively). The GG+GA genotype of CYP2R1 rs12794714 and AA+AG genotype of CYP2R1 rs10766196 were associated with prevalent vitamin D deficiency in children with type 1 diabetes. These genotypes did not differ with respect to glycosylated hemoglobin and daily insulin requirement. CONCLUSIONS: Serum 25OHD and 1α,25(OH) D levels were lower in children with type 1 diabetes than in healthy controls. CYP2R1 rs12794714 and rs10766196 polymorphisms were associated with a higher risk of type 1 diabetes. Thus, polymorphisms in vitamin D metabolism may contribute to susceptibility to type 1 diabetes in Korean children.