Dieulafoy lesions are uncommon sources of GI hemorrhage and predominantly occur in the proximal stomach. At one time a pathological diagnosis made postoperatively, Dieulafoy lesions are now routinely diagnosed and treated endoscopically. Their true incidence is unclear as quiescent Dieulafoy lesions are easily overlooked on endoscopy and bleeding lesions are occasionally misidentified. Over 6 yr (June 1993-November 1999), 40 Dieulafoy lesions were identified on upper endoscopy at our institution, of which seven were located in the duodenum and one in the right colon. Forty-seven percent of patients were hospitalized for other causes before onset of bleeding, and 17 of 40 were found to have other abnormal findings at endoscopy. In 90% of the cases, endoscopic treatment was successful. Seven patients died, but none as a result of hemorrhage. In 24 endoscopically-treated patients in whom follow-up data are available, Dieulafoy bleeding recurred in one patient. Dieulafoy lesions are rare and often difficult to diagnose, but must be considered in the evaluation of upper and lower GI tract hemorrhage, as they can usually be managed endoscopically.