Proximal deep venous thrombosis and pulmonary embolism should be treated for at least three months. The optimal duration then depends on the cause of venous thromboembolism (VTE). When VTE is provoked by a major transient risk factor like surgery, three month treatment dura- tion is sufficient. When VTE is provoked by a persistent major risk factor like cancer, treatment should be prolonged as long as the underlying risk-factor is present. The optimal treatment duration is more difficult to define after an episode of unprovoked VTE and when VTE is triggered by a minor risk factor like travel or oral contraceptives. In these circumstances, the risk of recur- rent VTE is still high after six months of anticoagulant treatment. Prolonging the anticoagulant treatment for an additional period of 12 to 24 months after the initial period of 6 months is associated with delayed recurrences but does not reduce the overall risk of recurrent VTE. In these patients, treatment should be stopped at six months or prolonged indefinitively according to the risks of recurrence and bleeding of the patient.