Factor XIII (FXIII) plays an important role in formation and stabilization of the fibrin clot. It is known that FXIII-A gene G163T (Val34Leu) polymorphism leads to increased activation of this factor, however participation of the 34Leu variant in thrombogenesis remains disputable. The present work was aimed at studying peculiarities of distribution of variants of FXIII-A polymorphisms in patients with early onset of venous thromboembolism (VTE), as well as revealing associative links between the carrier state of this mutation and the character of clinical course of the disease. We examined a total of 250 patients with VTE. Of these, there were 119 (47.6%) men and 131 (52.4%) women, mean age 37.42 years (range 10-45 years). In the group of patients with VTE, the proportion of homozygous carriers of allele 163T (Leu34) turned out to be more than 1.5-fold higher as compared with the corresponding parameter in the control group (OR=1.8, 95% CI: 0.9-4.0; p=0.14). Analysing FXIII-A G163T polymorphism depending on gender revealed a considerable increase in the incidence rate (IR) of 163TT genotype in women with VTE as compared to male patients (13.0% versus 5.1 %, respectively, OR=2.8, 95% CI: 1.1-7.4; p=0.047) and to the control group (OR=2.7; 95% CI: 1.2-6.1; p=0.023). Analysing gene FXIII-A polymorphism in the groups of patients with various clinical manifestations of VTE revealed a decrease in the proportion of heterozygotes in the group of deep vein thrombosis + pulmonary artery thromboembolism (PATE) and, vice versa, an increase in the proportion of homozygotes by the Leu34 variant in patients with signs of PATE. The obtained findings make it possible to consider the genotype 163TT of FXIII-A gene as a new independent risk factor for the development of VTE in young women living in the North-West region of Russia, which is observed for the first time. Additional studies are necessary.