In the past, patients with a first episode of DVT were usually treated for a fixed period of 3 months regardless of the underlying cause (18). Currently, there is a trend toward adjusting the duration of anticoagulation according to patients' clinical characteristics at baseline. Selected patients with permanent risk factors, such as active cancer, prolonged immobilization due to chronic medical illnesses, the antiphospholipid antibody syndrome, and other thrombophilic conditions, generally receive long (and sometimes lifelong) courses of oral anticoagulant therapy (1–2, 19). In most patients without permanent risk factors, anticoagulation is usually withdrawn after a shorter period, ranging from 6 months to 2 years in patients with idiopathic thrombosis (4, 6–7, 19–20) and from 6 to 12 weeks in those with transient risk factors (4, 19–20). However, in all patients, the risk for recurrence after a short, fixed period of anticoagulation varies greatly. Approximately 70% of patients with unexplained thrombosis do not develop a recurrence (3–7, 20), and 10% of patients with transient risk factors do (3–5, 20). Therefore, improving our ability to identify patients who are more likely to develop a recurrence might help clinicians individually tailor the duration of anticoagulation. This, in turn, would allow a more favorable risk–benefit ratio in the use of anticoagulant treatment.