INTRODUCTION. Trombotic complications are one of the leading causes of morbidity and mortality in patients with essential thrombocytaemia. When we compare arterial and venuos thrombosis, arterial thrombosis are more frequent. The most investigated risk factors for thrombosis are age, history of thrombosis, JAK2V617F mutation, cardiovascular risk factors, blood cells and markers of thrombophilia. To the present day, role of JAK2V167F mutation in patogenesis of thrombosis in patients with essential thrombocythaemia is variable. AIMS OF THE STUDY. Investigate frequency of thrombotic complications in patients with essential thrombocythaemia who had detected JAK2V617F mutation and compare with the frequency of thrombotic complications in patient with essential thrombocythaemia who had not detected JAK2V617F mutation. Investigate frequence of different type thrombosis, arterial and venuos, in JAK2V617F positive patients with essential thrombocythaemia. Examine correlations clinical risk factors and laboratory parameters with occurrence of thrombotic complications in JAK2V617F positive patients with essential thrombocythaemia. MATERIAL AND METHODS. Research was retrospective-prospective, in period between 2016-2021, situated in Clinic of Hematology and in Center of Laboratory Medicine in Clinical Center of Vojvodina. In research participate 95 patients with ET, who were divided into two groups according to presence or absence of JAK2V617F mutation. All patients were required to fill anamnesis and questionnaire which included data about risk factors (smoking, hyperlipoproteinaemia, hypertension, diabetes and treatment of comorbidity) for occurrence thrombotic complications and history of thrombosis. After this part, blood was sampled from all patients for laboratory analysis (ESR, CBC with platelets parameters, biochemical analysis, electrophoresis serum proteins, lipid status, lipoprotein A, hemostasis mechanism and markers of thrombophilia (protein C, protein S, antithrombin, resistance of activated protein C, anticardiolipin antibodies IgM, IgG, antibetaglycoproteins antibodies IgM, IgG, lupus anticoagulants and molecular analysis with PCR method for determining factor V Leiden, prothrombin G20210A and methylenetetrahydrofolate reductase)). All thrombotic incidents are divided into three groups: historic thrombosis, thrombosis at diagnosis and thrombosis during follow up. Statistical analyses were performed by IBM SPSS Statistics, Version 26.0. RESULTS: Thrombotic complications were registered in 26 (28.4%) patients with essential thrombocythaemia in both cohorts together. Arterial thrombosis was verified in 19 (20%) patients and venous thrombosis in 10 (10.5%) patients with essential thrombocythamia. All thrombotic complications, all venous thrombotic complications and historical venous thrombosis are more frequent in JAK2V617F positive patients with essential thrombocythaemia in comparison with JAK2V617F negative patients (<0.05). We did not confirm differences in frequency in arterial and venous thrombotic events in JAK2V617F positive patients (>0.05), neither in JAK2V617F negative patients with essential thrombocythaemia (>0.05). In analysis of cardiovascular risk factors (hypertension, hyperlipoproteinaemia, diabetes, smoking and presence at least on cardiovascular risk factor), hyperlipoproteinaemia was contributed to the occurrence of all thrombosis at diagnosis, especially arterial thrombosis in JAK2V617F mutation positive patients with essential thrombocythaemia. Hypertension and diabetes were contributed to the occurrence of all thrombosis at diagnosis, especially arterial thrombosis in JAK2V617F negative patients with essential thrombocythaemia. In analysis of laboratory parameters, hypertriglicidaemia positively correlated with occurrence of all thrombosis at diagnosis, regardless of presence JAK2V617F mutation. Hyperholesterolaemia (elevated nonHDL cholesterol) contributed occurrence of arterial thrombosis at diagnosis regardless of presence JAK2V617F mutation. There is no laboratory parameters that positively correlated with occurrence any thrombosis during follow up in patients with essential thrombocythaemia. CONCLUSIONS: JAK2V617F mutation has important role in occurrence of thrombotic complications. Cardiovascular risk factors and laboratory finding of hyperlipoproteinaemia significantly affect on occurrence of thrombotic complications, especially arterial at diagnosis in patients with essential thrombocythaemia. Role of laboratory analysis such as count of white blood cells, count of platelets, genetic mutations for inherited thrombophilia and other markers of thrombophilia, do not have role in occurrence of thrombotic complications during follow up in patients with essential thrombocythaemia.