The purpose of this study is to determine if the risk of recurrent venous thromboembolism (VTE) after stopping therapy is low and acceptable in patients with a first unprovoked proximal deep vein thrombosis (DVT) or pulmonary embolism (PE) who have completed 3 months of therapy and who have a negative D-dimer test on therapy and 1 month after stopping therapy.

Inclusion Criteria:

1. Be >= 18 years of age
2. Have had ONE episode of unprovoked proximal DVT and/or PE
3. Have completed 3 uninterrupted months of warfarin therapy (target INR of 2.0-3.0)

Exclusion Criteria:

1. Another indication for long-term anticoagulation (e.g., atrial fibrillation)

2. A high risk of bleeding as evidenced by any of the following:

   • Age greater than 75 years
   • Previous episode of major bleeding where the cause was not effectively treated
   • Known chronic thrombocytopenia with a platelet count of less than 120,000 x 10^9 /L
   • Known chronic renal impairment with a creatinine of more than 150 mumols /litre (1.7 mg/dl)
   • Known chronic liver disease with a total bilirubin of more than 25 mumols /litre (1.5 mg/dl)
   • Active peptic ulcer disease
   • Poor compliance with, or control of, anticoagulant therapy during initial treatment
   • Requires dual antiplatelet therapy (e.g. aspirin and clopidogrel)

3. A vena caval filter

4. Has had D-dimer testing performed within 2 months of potential enrollment other than for evaluation of suspected recurrent VTE that was not confirmed

5. Has a life expectancy less than 5 years

6. Is unable to attend follow-up visits because of geographic inaccessibility

7. Is participating in a competing clinical investigation