Objective: To investigate the frequency of HLA system alleles and haplotype connections in patients with positive and negative family history of Hashimoto's thyroiditis as well as psoriasis. Materials and methods: Nine family members from mother’s and father’s side of the test subject were tested using the serological method of microlymphocytotoxicity and the molecular method PCR-SSO. Results: The HLA-B*35 allele, which is responsible for Hashimoto's thyroiditis, was found to be passed on from the father's side and inherited by three out of the four children. HLA-B*13, -B*17, -DRB1*07 alleles were observed on the mother's side, which are closely correlated with psoriasis. Conclusion: The HLA system is highly associated with genetically inherited diseases, including Hashimoto's thyroiditis and Psoriasis vulgaris. The presence of the genes responsible for these two diseases within the family was established. This paper shows that family studies have favorable characteristics for gene discovery because they represent a more homogeneous and limited set of causative genes and pathways.