AIM: Acute gastrointestinal bleeding is a severe complication in patients receiving long-term oral anticoagulant therapy.The purpose of this study was to describe the causes and clinical outcome of these patients.METHODS: From January 1999 to October 2003, 111patients with acute upper gastrointestinal bleeding (AUGIB)were hospitalized while on oral anticoagulants. The causes and clinical outcome of these patients were compared with those of 604 patients hospitalized during 2000-2001with AUGIB who were not taking warfarin.RESULTS: The most common cause of bleeding was peptic ulcer in 51 patients (45%) receiving anticoagulants compared to 359/604 (59.4%) patients not receiving warfarin (P＜0.05). No identifiable source of bleeding could be found in 33 patients (29.7%) compared to 31/604(5.1%) patients not receiving anticoagulants (P= 0.0001).The majority of patients with concurrent use of non-steroidal anti-inflammatory drugs (NSATDs) (26/35, 74.3%) had a peptic ulcer as a cause of bleeding while 32/76 (40.8%)patients not taking a great dose of NSATDs had a negative upper and lower gastrointestinal endoscopy. Endoscopic hemostasis was applied and no complication was reported.Six patients (5.4%) were operated due to continuing or recurrent hemorrhage, compared to 23/604 (3.8%) patients not receiving anticoagulants. Four patients died, the overall mortality was 3.6% in patients with AUGIB due to anticoagulants, which was not different from that in patients not receiving anticoagulant therapy.CONCLUSION: Patients with AUGIB while on long-term anticoagulant therapy had a clinical outcome, which is not different from that of patients not taking anticoagulants.Early endoscopy is important for the management of these patients and endoscopic hemostasis can be safely applied.