The researchers randomly assigned patients to a fixed- or flexible-duration, ultrasonography-guided treatment strategy. Depending on the underlying cause of the DVT, patients in the fixed-duration group received either no additional treatment or 3 more months of anticoagulation (warfarin). Patients in the flexible-duration group had no further treatment if ultrasonography showed dissolved leg clots (recanalized veins) and continued anticoagulation with warfarin for 9 to 21 months if repeated ultrasonography showed persistent clots (residual thrombosis). The researchers followed patients for 33 months to assess recurrent clots and bleeding complications.