Rendu-Osler-Weber disease, or hereditary hemorrhagic telangiectasia (HHT), is an autosomal dominant disorder with incomplete penetrance, characterized by vascular anomalies which may virtually develop in many organs. The prevalence varies and may range from 1/3,500 to 1/5,000 in specific regions. Two chromosal sites have been at least identified: in HHT1, mutations at chromosome 9 alter the protein endoglin and in HHT2, mutations at chromosome 12 alter the protein activine or ALK-1. Clinical manifestations include recurrent epistaxis, mucocutaneous telangiectases that bleed easily, and larger arteriovenous malformations in parenchymatous organs. Epistaxis is the first symptom, occurring in the vast majority of affected persons. The lung is the most common site for arteriovenous malformations. Brain abscess, transient ischemic attack and ischemic stroke occur exclusively in patients with pulmonary arteriovenous malformations and right-to-left shunt, which facilitates the passage of emboli into the cerebral circulation. Transcatheter embolotherapy with detachable balloons or stainless-steel coils has been used in order to occlude such malformations and to prevent such complications. At present a genetic diagnosis is possible in only a few families. The clinical diagnosis is based on 4 criteria: family history, epistaxis, mucocutaneous telangiectases and arteriovenous malformations. The diagnosis will be definite if 3 criteria are present, suspected if 2 criteria are present, unlikely if fewer than 2 criteria are present. In conclusion, the authors examine clinical features of 28 HHT patients observed in the HHT University Centre of Bari from September 2000 to May 2001.