It takes about 3 months to complete "active treatment" of venous thromboembolism (VTE), with further treatment serving to prevent new episodes of thrombosis ("pure secondary prevention"). Consequently, VTE should generally be treated for either 3 months or indefinitely (exceptions will be described in the text). The decision to stop anticoagulants at 3 months or to treat indefinitely is dominated by the long-term risk of recurrence, and secondarily influenced by the risk of bleeding and by patient preference. VTE provoked by a reversible risk factor, or a first unprovoked isolated distal (calf) deep vein thrombosis (DVT), has a low risk of recurrence and is usually treated for 3 months. VTE associated with active cancer, or a second unprovoked VTE, has a high risk of recurrence and is usually treated indefinitely. The decision to stop anticoagulants at 3 months or to treat indefinitely is more finely balanced after a first unprovoked proximal DVT or pulmonary embolism (PE). Indefinite anticoagulation is often chosen if there is a low risk of bleeding, whereas anticoagulation is usually stopped at 3 months if there is a high risk of bleeding. The decision to continue anticoagulation indefinitely after a first unprovoked proximal DVT or PE is strengthened if the patient is male, the index event was PE rather than DVT, and/or d-dimer testing is positive 1 month after stopping anticoagulant therapy.