HLA-DQ haplotypes in celiac disease patients and celiac disease patients with associated type 1 diabetes Aim of the research: To determine the frequency of HLA-DQ haplotypes with regard to gender and age in the group of patients with celiac disease and the group of patients with celiac disease associated with T1DM. Examine the differences in the frequency of HLA-DQ haplotypes with respect to gender and age at the time of disease diagnosis. Study design: Cross-sectional study with historical data. Patients and methods: The groups of participants are patients whose HLA typing was performed from 1.1.2009. to 1.3.2023. at the Laboratory for Molecular and HLA Diagnostics of the University Hospital Osijek. Fifty patients with a diagnosis of celiac disease and 9 patients with a diagnosis of celiac disease associated with T1DM were identified. Results: The group of patients with celiac disease consisted of 29 women (58 %) and 21 men (42 %), while the group of patients with celiac disease and T1DM consisted of 7 women and 2 men. The majority of patients diagnosed with celiac disease were between 0 - 5 years old (58 %), while those diagnosed with celiac disease associated with T1DM were between 13 - 23 years old. The most frequent allele variants in patients with celiac disease were HLA-DQA1*05 (50 %) and HLA-DQB1*02 (46 %). The most frequent allele variants in patients with celiac disease and T1DM were HLA-DQA1*01 and HLA-DQB1*02. The most frequent haplotype in patients with celiac disease was HLA-DQ2.5 (35 %) . Conclusion: HLA-DQA1*05 and HLA-DQB1*02 are the most frequent allele variants in patients with celiac disease. HLA-DQA1*01 and HLA-DQB1*02 are the most frequent allele variants in patients with celiac disease and T1DM. The most frequent haplotype in patients with celiac disease is HLA-DQ2.5, and the most frequent genotype is DQ2.5/DQX. The most frequent haplotype in patients with celiac disease and T1DM is DQA1*01-DQB1*06, and the most frequent genotype is DQX/DQX.