Thrombophilia testing is now commonplace. However, testing for heritable thrombophilia does not predict outcome in response to oral anticoagulant therapy. At present there is no conclusive evidence that recurrence on treatment with warfarin with a target International Normalized Ratio of 2.5 is greater in patients with laboratory evidence of heritable thrombophilia compared with those without. Similarly, there is no conclusive evidence that patients with laboratory evidence of heritable thrombophilia are more likely to suffer an earlier recurrence once treatment is stopped. Therefore, the management of patients with familial thrombotic disease and patients with laboratory evidence of heritable thrombophilia should be influenced by their personal and family history rather than the results of laboratory investigations. There is no doubt that the relative risk of thrombosis is increased in affected family members of thrombosis-prone families but this translates to a relatively low absolute risk per year, and long-term primary prophylaxis with oral anticoagulant therapy is not justified in the majority. Evidence of antiphospholipid syndrome is associated with an increased risk of recurrent venous thromboembolism, but there is still uncertainty as to the optimal intensity and duration of oral anticoagulant therapy after an episode of arterial or venous thrombosis in patients with detectable antiphospholipid activity.