Vitamin K antagonists are the mainstay for the treatment for venous thromboembolism. The optimum (VTE) course of oral anticoagulant therapy is determined according to the risk of recurrent VTE after stopping anticoagulant therapy and the risk of anticoagulant-related bleeding while on antivitamin K. The risk of recurrent VTE is low when the initial episode is provoked by a reversible major-risk factor (surgery), whereas this risk is high when VTE is not provoked or associated with a persistent-risk factor (cancer). Conversely, the influence of biochemical and morphological tests is uncertain. The optimum balance of the benefits and the risks of oral anticoagulant therapy is based on the frequency as well as the consequences of the risk of recurrent VTE and anticoagulant-related bleeding. After VTE provoked by a major reversible-risk factor, three months of anticoagulation is optimal, whereas after unprovoked VTE, anticoagulation should be extended. However, given the number of unresolved issues, a randomised trial comparing different durations of anticoagulation is needed.