In principle, the answer to this question is obvious: "as long as the risk of continued therapy is outweighed by the benefit." In practice, determining an individual patient's risk of recurrent venous thromboembolism (VTE) without warfarin or other vitamin K antagonists is difficult. However, there are many factors (both intrinsic and environmental) that can alter the risk of VTE recurrence. This paper will discuss evidence and considerations (including the issue of bleeding risk) that may be relevant to decisions about duration of anticoagulant therapy for patients with VTE.