This 1st report of the occurrence of arteriovenous fistula of the lung in siblings shows that it is a congenital inherited anomaly, occurring in both sexes and transmitted as a dominant with incomplete penetrance. It is a manifestation of hereditary hemorrhagic telangiectasia. A previously reported case diagnosed as a pulmonary arteriovenous fistula was confirmed at operation and cured by pneumonectomy. A new case is reported.