Study outcomes and Follow-up. From the assignment visit, patients will be followed up for at least one year after OAT discontinuation; during the follow-up period, patients will be contacted by the clinical centers every 3 months. C-US will be performed only when recurrent symptomatic DVT is suspected. The study outcome is the composite of confirmed recurrent venous thromboembolism (including DVT and/or fatal or non-fatal pulmonary embolism) and major bleeding events from the index DVT to the last day of follow-up. In cases of suspected DVT recurrence the results of ultrasonography will be compared with the previous examination. A diagnosis of recurrent venous thrombosis is made if a previously fully compressible segment (contralateral or ipsilateral) became incompressible. In absence of a previous normal C-US, DVT recurrence is diagnosed if a previously non-occlusive thrombus shifted to occlusive thrombus, provided the vein area before compression had increased by more than 50%); in undetermined cases, contrast venography was performed. In patients with suspected pulmonary embolism, diagnosis of recurrence is based on objective algorithms using clinical probability, ventilation-perfusion lung scanning/helical computed tomography, compression ultrasonography and/or D-dimer if indicated. The diagnosis of clinically relevant haemorrhage will be made in case of decrease of haemoglobin levels > 2.0 gr/dl, retroperitoneal, intracranial or life-threatening. Patients has been instructed to contact the clinical center immediately if symptoms developed suggestive of venous thromboembolism or bleeding. All suspected outcome events and all deaths will be evaluated by a central adjudication committee whose members were unaware of the name of the subject, the enrolling center, the C-US findings and the assigned group.