Laparotomy performed for bleeding duodenal ulcer after diagnostic/therapeutic endoscopy revealed a disparity in location of the lesion on several occasions at our institution. The position of the duodenal lesion is important in assessing bleeding potential. Twenty consecutive patients underwent upper gastrointestinal endoscopy by a staff and trainee gastroenterologist to evaluate the ability to determine the true posterior position of the duodenal bulb. Documentation of the posterior bulb location was verified by pooled colored fluid with the patient in a supine position. True posterior location was chosen only 30% of the time by an experienced gastroenterologist. This observation may have clinical implications in assessing the patient's bleeding potential and in the use of coaptive coagulation for control of ulcer bleeding.