We report a Chinese lady with hereditary hemorrhagic telangiectasia who presented with multiple episodes of gastrointestinal bleeding requiring transfusion. Gastroscopy, colonoscopy, isotope-labeled red blood cell scan, and selective arteriography were performed, but could not locate the source of bleeding. A bleeding lesion in the ampulla of Vater was seen when endoscopic retrograde cholangiopancreatography was attempted. She had an uneventful pylorus-preserving Whipple's operation with no further evidence of gastrointestinal bleeding. This is the first case report to show that the vascular ectasia of patients with hereditary hemorrhagic telangiectasia could manifest at the ampulla of Vater.