Thrombosis is a complex disorder involving interaction between many different types of genes with environment factors. Modification in genes coding for coagulation and regulatory proteins of hemostasis are important risk factors for thrombosis. Historically, the measurement of a clot endpoint has been the basis of coagulation testing mainly focused on bleeding disorders. Thrombosis diagnosis has slowly increased with most modern automated coagulation instruments utilizing optic, immunologic, and chromogenic methods. However, molecular diagnostics has added another dimension for the evaluation of clotting and bleeding disorders. DNA-based tests are commonly available for the detection of the factor V Leiden mutation, the prothrombin 20120A mutation, and the methyltetrahydrofolate reductase mutation.