A patient with hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome) with multiple bilateral pulmonary arteriovenous malformations was hypoxic, cyanotic, polycythemic, and severely limited by dyspnea on exertion. Following staged bilateral thoracotomies, with removal of 23 major fistulas (12 from the right lung and 11 from the left), marked improvement in symptoms, blood gases, and objective measurements of exercise tolerance occurred.