Myeloproliferative neoplasms (MPN) are haematological diseases, characterized by clonal hematopoiesis. Hemostasis abnormalities are among the most critical and frequent complications, affecting the quality of life and a possible reason for death. Thrombotic complications are common and multifactorial. Our aim was to study some genetic thrombophilia factors – Factor V Leiden (FVL), G20210A mutation in prothrombin gene (PR G20210A) and PLA2 allele polymorphism of glycoprotein IIIa gene (GPIIIa gene), and their frequency and association with thrombotic risk in both Philadelphia-positive and Philadelphia-negative MPN – chronic myelogenous leukemia (CML), polycythemia vera (PV), essential thrombocythemia (ET), and primary and secondary myelofibrosis (MF). In our patient population, PLA2 allele polymorphism of GPIIIa gene proved to be the most common and significantly associated with thrombotic complications – 26.85% of our patients were carriers, and 24.14% of them reported thrombotic complications.