Why include all bleeding, and how is this endpoint defined ? Previous studies of both antithrombotic treatment and the treatment of warfarin-associated coagulopathy have used only major hemorrhage as the measure of bleeding. In those studies, "major hemorrhage" has been chosen as the primary measure because it is both detected and independently adjudicated more easily than "all hemorrhage". In addition, in most such studies of antithrombotic therapy, patients with acute thrombosis (or those at high risk of acute thrombosis) are enrolled. In the setting of acute thrombosis it is likely that physicians and patients are willing to tolerate minor bleeding as one of the "unavoidable" complications of antithrombotic therapy. Neither patients nor physicians would be willing to stop an effective treatment for acute, life threatening thrombosis because of minor bleeding. In the setting of warfarin maintenance therapy, however, minor bleeding such as unanticipated bruising, epistaxis or excessive menstrual blood loss in the setting of an excessively prolonged INR value is disconcerting, disruptive, costly if patients seek medical attention and likely to reduce compliance. Since we believe that reducing all bleeding complications (major and minor) is necessary to maximize the utility of warfarin therapy, we have chosen to measure all bleeding as our primary outcome measure of efficacy. We feel this is appropriate since the study intervention is masked; thus although minor bleeding is subjective, patients should be unaware of their treatment allocation and thus the treatment they receive will not influence their reporting of clinical events.