To assess whether 1,25(OH)2D3 status has an impact on the expression of CYP24A1 and CYP27B1 in PBMCs of T1DM patients and the healthy control, we analyzed the correlation between serum 1,25(OH)2D3 levels and the expression levels of CYP24A1 and CYP27B1. This evidence concerns the gene CYP24A1 and type 1 diabetes mellitus.