Exclusion criteria: missing data during the follow-up; contraindications to or lack of compliance to oral anticoagulation (OAT), lack of informed consent; history of previous VTE event; indication for continuous oral anticoagulation (e.g., an artificial heart valve or chronic atrial fibrillation); events occurring during pregnancy, malignancy, puerperium, oral contraceptive intake, hormone replacement therapy; deficiencies of Prot. C and Prot S or combined inhibitor deficiencies.