Type 1 diabetes mellitus (T1DM) is one of the long-time studied autoimmune disorders. The triggering of the autoimmune process has been ascribed to various genes active in the regulation of the cytokine gene transcription including the Rel/NF-kappaB gene family. In our study the gene polymorphism of HLA class II, NFKB1 (nuclear factor of kappa light polypeptide gene enhancer in B-cells 1) and NFKBIA (inhibitor of nuclear factor kappa B) was tested. Patients were divided into the subgroups in relation to the disease type: T1DM in children, T1DM in adults, and Latent Autoimmune Diabetes in Adults (LADA). HLA-DRB1 (*)04 and HLA-DQB1 (*)0302 have been detected as risk factors for T1DM in adults and particularly in children (P<0.0001, OR=22.9 and 46.5 respectively). HLA-DRB1 (*)03 has been found as a single risk factor for LADA (P<0.0001, OR=4.9). We detected 15 alleles for the NFKB1 gene polymorphism (CA-repeats) in the Czech population. The alleles were ranging in size from 114-142 bp corresponding to 10-25 CA repeats. Frequency of the A7 allele of NFKB1 gene has been significantly increased in T1DM adults (P<0.01). There was no difference in A and a G allele frequency of NFKBIA gene between the control group and patients, but the association of the AA genotype of NFKBIA gene has been found for LADA (P<0.05). Summarizing our results we concluded that there is a high probability of association of gene polymorphism from Rel/NF-kappaB family with an autoimmune diabetes course. Due to the results obtained in the epidemiological study we have been looking also for the function significance of the genetic predisposition. No significant changes have been observed by real time PCR testing of HLA-DRB1 (*)04 gene and NFKB1 gene expression between T1DM diabetic group with different HLA, NFKB1, NFKBIA genetic background.