Hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu disease) is an autosomal dominant, systemic fibrovascular dysplasia in which telangiectases, arteriovenous malformations, and aneurysms may be widely distributed throughout the body vasculature. Major clinical manifestations include: recurrent bleeding from mucosal telangiectases and arteriovenous malformations; hypoxemia, cerebral embolism, and brain abscess due to pulmonary arteriovenous fistulas; high-output congestive heart failure and portosystemic encephalopathy from hepatic arteriovenous malformations; and a variety of neurologic symptoms due to central nervous system angiodysplasia. Therapy is primarily supportive, consisting of iron supplementation and blood transfusion. Septal dermoplasty and oral estrogens may allow prolonged remission of epistaxis, but permanent surgical cure of gastrointestinal bleeding is rarely feasible because of diffuse angiodysplasia of the alimentary tract. Ligation, resection, or embolization may be indicated for pulmonary arteriovenous fistulas. The prognosis and survival of patients with hereditary hemorrhagic telangiectasia are favorable, providing treatable complications are accurately diagnosed.