Thrombotic complications often complicate the course of the underlying disease in patients with chronic myeloproliferative neoplasia. However, a thromboembolic condition is not observed in all patients.The aim of the study was to assess the carriage frequency of polymorphic genes of the blood coagulation system and folate metabolism genes and the contribution of genetic variants to the development of thrombosis in patients with chronic Ph-negative myeloproliferative neoplasia (CMPN).Materials and methods. Molecular genetic testing for the presence of genetic variants with an assessment of their frequency of occurrence and allelic load was carried out in 142 patients with CMPN. We studied polymorphisms of the folate cycle genes – A2756G (Asp919Gly) of the MTR gene, C677T (Ala22Val) of the MTHFR gene, A66G (ILe22Met) of the MTRR gene (rs1801394), as well as mutations of the genes of blood coagulation factors – G(455)A of the FGB gene, G20210A of the F2 gene, G10976A (Arg353Gln) of the F7 gene, G1691A (Arg506Gln) of the F5 gene. The study was carried out using real-time polymerase chain reaction (PCR); The biological material for the test was whole blood.Results and discussion. The study showed that only 6 out of 50 (12%) patients with thrombotic complications had no changes in the genes studied, while 88% of patients had one or another genotypic variant, which may indicate a high probability of involvement of a hereditary genetic factor in the development of hypercoagulability and thrombotic complications in patients with chronic MPN.Conclusions. A comprehensive study of the role, interaction and operating conditions of genes that control blood coagulation processes in patients with Ph-negative chronic MPN will make it possible to understand the causes of hemostatic system disorders and develop effective measures to prevent thrombotic complications in this category of patients.