Rendu-Osler disease, hereditary hemorrhagic telangiectasia is a genetic disorder, autosomal dominent. Telangiectasia of the skin, face, trunk, upper and lower extremities are associated with angiomas of the oral and nasopharyngal membranes, lips, tongue and internal organs (intestine tract, liver, spleen, blood, lung, brain). They are source of melena, hematemesis, hematuria, hemoptysis with severe anemia. RESULTS dilated blood vessels forming cavernous spaces, flattened endothelial cells, no perivascular infiltration, degeneration of the perivascular connective tissue, elastic and muscular fibers missing around the vessels. Therefore hemorrhages are not able to stop spontaneously. Ultrastructural changes : formation of gaps along the thinned-out endothelial lining of dilated vessels, gaps plugged with thrombi. Anormal perivascular collagenous tissue, perivascular smooth muscles elongated and irregular in shape, did not surround the vessels. Liver cirrhosis and blood loss (gastrointestinal hemorrhages sometimes massive) are the only digestive manifestation of the severity. Systematic replacement of iron and blood transfusions are the most helpful forms of treatment.