Objective[|]Major causes of mortality in patients with valvular disease are endocarditis and valve thrombosis. Oral anticoagulant drugs are used to prevent valve thrombosis. Uses of inadequate doses of medication or absence of medication use are the main reasons for the development of valve thrombosis. In addition to medical treatment or surgical treatment of patients with infective endocarditis has a high mortality rate. In this study, MTHFR C677T, Prothrombin (Factor-II) G20210A, Factor-V Leiden G1631, PAI-1 4G/5G and TNF-α-308 G>A were determined in patients with infective endocarditis and valve thrombosis groups.[¤]Materials and Methods[|]18 patients with infective endocarditis, 12 patients with valve thrombosis and 37 healthy volunteers were included in this study. Polymerase chain reactions (PCR) and restriction fragment length polymorphisms (RFLP) were used to detect the related polymorphism. Chi-square was used to compare groups.[¤]Results[|]There were no significant differences between the groups regarding MTHFR C677T, Prothrombin (Factor-II) G20210A, Factor-V Leiden G1631, PAI-1 4G/5G polymorphism. In contrast, a significant difference was found in TNF-α -308 G>A polymorphism between the groups.[¤]Conclusion[|]In our study, TNF-α-308 G>A results were higher in patients with endocarditis and valve thrombosis than control groups in chi-squares test and there were significant differences between two groups. There is not enough data in literature about the involvement of genetic factors in valve thrombosis. For this reason, larger and more comprehensive studies are needed.[¤]