It has been reported that HLA DR3/DR4 genotype confers the strongest genetic risk for T1D, however, in our Spanish cohort the highest risk genotype for T1D is DRB1*03/DRB1*03 (RR = 22.19 vs. RR = 15.11 for DRB1*03/DRB1*03 and DRB1*03/DRB1*04, respectively; considering RR = 1 subjects negatives for these alleles). This evidence concerns the gene HLA-DRB1 and type 1 diabetes mellitus.