Autoimmune thyroid disease (AITD) is caused by an immune response to self-thyroid antigen. The cytotoxic T-lymphocyte antigen-4 (CTLA4) gene, encoding a negative regulator of the T-lymphocyte immune response, had been reported to be associated and/or linked to AITD. The aim of the study was to investigate the association between the exon 1 CTLA-4 gene polymorphism A(49)G and susceptibility to graves’ disease (GD) and Hashimotos thyroiditis (HT). Materials and methods. We analyzed the A(49)G exon 1 CTLA-4 gene polymorphism in 105 unrelated Novosibirsk patients with GD, in 101 patients with HT and 150 matched healthy subjects. Results. The distribution of genotype frequencies differed significantly between patients with GD and controls (p = 0.039). The allele G and the genotype GG were associated with the increased risk for GD (odds ratio OR = 1,55, 95% CI, 1,09—2,21, OR = 2,43, 95% CI, 1,17—5,01 respectively). In contrast, no differences in genotype frequencies were observed between HT patients and controls for the A(49)G exon 1 CTLA-4 gene polymorphism. Conclusion: This suggests that the CTLA-4 gene might play a role in the development of DTS in the Novosibirsk population.