Testing for laboratory evidence of heritable thrombophilia is now common. This practice undoubtedly arose in response to association studies, which revealed the influence of heritable thrombophilic defects on the development of VTE. Now that high quality clinical outcome studies are being reported it is becoming apparent that despite association, testing has limited predictive value for the majority of unselected symptomatic patients. Clearly, there is a difference between the ability of a test to explain why one individual is more likely to suffer a thrombosis than another and the ability of the same test to predict which patients who have already had thrombosis are likely to suffer a recurrence. In the absence of grade A recommendations, it is inevitable that practice will vary. Decisions will be influenced by local resources, competing demands for clinical and laboratory services and not least the professional interest of the haematologist. If thrombophilia testing is performed there is a strong case for selecting patients for testing as in most cases decisions regarding intensity and duration of anticoagulant therapy can be made purely in relation to clinical criteria. Copyright (C) 2004 S. Karger AG, Basel.