Dieulafoy's lesion is a vascular anomaly generally located in the proximal stomach, although it has also been documented in other areas such as the colorectum. It is mainly found in men aged between 50 and 70 years, and represents less than 2% of acute gastrointestinal hemorrhagic episodes.A 66-year-old woman who was undergoing oral Diclofenac treatment presented with black stools. Endoscopy revealed acute duodenal erosions with no signs of bleeding. Black stools persisted after Diclofenac was discontinued and omeprazole treatment was started and the patient was admitted to hospital after 7 days. Colonoscopy revealed active bleeding in the upper colon, which ceased after sclerosis with ethanolamine oleate. The patient was discharged from hospital but was readmitted 10 days later because of rebleeding. The results of upper endoscopy were normal and colonoscopy performed 3 days later detected neither lesions nor bleeding. The pathogenesis of Dieulafoy's lesion is not well known, although it could be caused by erosion of the mucous lining of a vessel. Definitive diagnosis is histologic, although certain endoscopic diagnostic signs have been described. Endoscopic diagnosis is sometimes difficult; in such cases, arteriography should be employed, both for diagnostic and therapeutic purposes. The treatment of choice is endoscopic and the use of two hemostatic methods is advisable. If these procedures fail, surgery is required. Arteriography is the most suitable alternative in patients who are poor candidates for surgery.