Identified nearly a century ago, hereditary hemorrhagic telangiectasia, or Rendu–Osler–Weber syndrome, has long been viewed as a rare condition producing minor discomfort for affected persons. However, this disorder is now considered to be more common than previously thought,¹–⁵ and the associated brain and pulmonary lesions are sources of substantial morbidity and mortality.³,⁶–⁸ Wider recognition of the condition and awareness of its sequelae can help avoid the considerable risks associated with its mismanagement. Advances in molecular genetics have demonstrated that hereditary hemorrhagic telangiectasia is actually a group of autosomal dominant disorders.⁹–¹³ The recent identification of the gene . . .