Hereditary Hemorrhagic Telangiectasia (HHT) is an autosomal-dominantly-inherited vascular dysplasia characterized by age-dependant incomplete penetrance and variable expressivity, with clinical manifestations consisting in epistaxis, mucocutaneous telangiectases, gastrointestinal bleeding and arteriovenous malformations (AVMs), which affects approximately Yz million people world-wide. It affects males and females of all racial and ethnic groups. Up to Ih of HHT patients have multiple organ involvement, which can be disabling and/or life threatening. HHT can be treated successfully if correctly diagnosed. Morbidity of HHT is often due to complications of AVMs, such as stroke or haemorrhage, also known to occur in children. Many authors have reported successful new therapeutical options for AVMs, which have resulted in a significant decrease of life-threatening complications and HHT morbidity. Since early diagnosis permits an appropriate care of affected subjects, a very sensitive mutation screening technique is required to identify the mutation carriers among all at-risk individuals belonging to HHT-families. There may be one or more genes that cause HHT but, if so, they are quite rare. Currently, scientists are trying to better understand exactly how the abnormal gene can interfere with normal blood vessel formation and promote the phenotype of HHT, so that better treatments for the symptoms of HHT can be developed.Hereditary hemorrhagic telangiectasia (HHT), also known as Rendu-Osler-Weber syndrome, is an autosomal-dominant disorder in which abnormal communications between arteries and veins, the so-called teleangiectases, occur in skin, mucosal surfaces and solid organs. Telangiectases often "break" and bleed after slight trauma. Spontaneous and recurrent epistaxis is the most common symptom. It begins by the age of 10 years and tends to be increasingly frequent as the time goes by.It may compromise/damage the patient's quality of life and cause anemia, requiring oral iron supplementation or blood transfusions. Moreover, affected patients can suffer from chronic blood loss, hypoxemia, hepatic dysfunction and high-output cardiac failure. HHT is an uncommon disease with a prevalence of 1:8000 (1), even if it is probably underdiagnosed in affected individuals because of