Massive upper gastrointestinal haemorrhage may be caused by ulcus simplex Dieulafoy. Of 144 patients consecutively operated on for benign gastric ulcer in 1975-1980, 29 were admitted as emergencies because of massive bleeding from the stomach. Six had the Dieulafoy lesion. Identification of the source of bleeding was made by fibreoptic endoscopy in five of these cases, while wide gastrotomy was required in one case. All were successfully treated, one with gastroscopic coagulation and the others surgically. Hitherto there has been no recurrence of bleeding. Diagnostic and therapeutic problems are described. The Dieulafoy lesion may be life-threatening. A century after it was first reported, reminder of the lesion is still necessary, since it probably is more rarely recognized than rare.