Study Design. This is a multicenter prospective study in patients with a first episode of symptomatic (either provoked or idiopathic) proximal DVT detected by Compression UltraSonography (C-US) and receiving OAT [warfarin (Coumadin, Bristol Myers Squibb) for 3 months. At this time, subjects who agreed to participate in the study have a physical examination to assess baseline clinical conditions and to exclude contraindications. C-US of the proximal deep vein system in both legs will be performed, measuring the diameters of any detectable thrombus in the Common Femoral Vein (CFV) and Popliteal Veins (PV). Images will be obtained in transverse section only. Lumen compressibility will be then evaluated on CFV and PV by gentle pressure of the probe, as previously described. Briefly, the major and the minor diameters of the vein segment are measured and recorded before and after compression. C-US findings are scored as “absence of RVT” when residual thrombus occupied, at maximum compressibility, less than 40% of the vein area. Patients without RVT will not continue anticoagulation, whereas those with RVT will be randomized to either stop or continue OAT (INR 2.0-3.0) for additional 9 months. A different randomization sequence for each different study site is computer generated and encapsulated in a randomization computer program. The sequences are balanced by blocks of ten.