Several polymorphisms in regions where Th1 cytokines (IL12B and IFNG genes) are located were analyzed in 303 Spanish subjects with type 1 diabetes and compared with a control cohort (n = 548). Both groups comprised residents of the Madrid area. The haplotype frequencies were estimated by the expectation-maximization algorithm, and p values were corrected by the number of haplotypes taken into account in the study. Two haplotypes were significantly associated with the disease, one in the IL12B region (D5S2038*8/D5S1352*2/SNP1188C; OR = 3.01, p(c) = 0.0255) and another involved the IFNGgene (D12S313*9/IFNG*1; OR = 1.58, p(c) = 0.0217). Furthermore, a protective IL12B haplotype was found (D5S2038*4/D5S1352*1/SNP1188A; OR = 0.40, p(c) = 0.0405). No association was found for any of IL12B and IFNG markers individually.