Thrombophilia is found in many patients presenting with venous thromboembolism (VTE). However, whether the results of such tests help in the clinical management of such patients has not been determined. Thrombophilia testing in asymptomatic relatives may be useful in families with antithrombin, protein C, or protein S deficiency or homozygosity for factor V Leiden, but is limited to women who intend to become pregnant or who would like to use oral contraceptives. Careful counseling with knowledge of absolute risks helps patients in making an informed decision in which their own preferences can be taken into account. Observational studies show that patients who have had VTE and have thrombophilia are at most at a slightly increased risk for recurrence. In an observational study, the risk of recurrent VTE in patients who had been tested for inherited thrombophilia was not lower than in patients who had not been tested. In the absence of trials comparing routine and prolonged anticoagulant treatment in patients testing positive for thrombophilia, testing for such defects to prolong anticoagulant therapy cannot be justified. Diagnosing antiphospholipid syndrome (APS) in women with recurrent miscarriage usually leads to treatment with aspirin and low-molecular-weight heparin (LMWH), although the evidence to support this treatment is limited. Because testing for thrombophilia serves a limited purpose, this test should not be performed on a routine basis.