Solitary exulceratio simplex (ulcer of Dieulafoy--Dieulafoy vascular malformation) is a rare and frequently overlooked cause of massive gastric hemorrhage. The source of the bleeding, a large, submucosal artery penetrating the centre of a small mucosal defect, is usually located in the upper portion of the stomach. The pathogenesis of this entity is not known. We report on two patients who were successfully treated by surgery. Clinical, morphological and pathogenetic aspects are discussed.