The chapter on angiodysplasias of the gastrointestinal tract raises numerous, still problematic, issues: - classification of the disorder (its clinical presentation and classification) - its anatomo-pathological identification - diagnosis of its nature and localization - treatment of patients with acute massive bleeding - long-term outcomes The possibility that an angiodysplasia underlies a bleeding event, even serious, makes this a timely topic. The exiguity of the lesion responsible for bleeding entails noteworthy diagnostic difficulties. By contrast, the relative rarity of such events, as well as of pertinent evidence in literature, do not allow a better understanding of the disease or, above all, its management. Nevertheless, it is important to bear the disorder in mind when faced with massive bleeding of unknown origin.