It is my purpose in this paper to call attention to the possibility of hydatid disease originating in American born persons and to collect the cases of the cysts of the lung due to infestation with Taenia echinococcus that have been reported in North America. In an address before the Clinical Congress of the American College of Surgeons at Montreal in 1926, Barnett1 made the statement that hydatid disease is increasing so rapidly in some of the South American countries as to constitute a national peril. In 1922, N. H. Fairley2 said that there had been no reduction during the preceding ten years in the number of cases admitted to the Melbourne hospitals. Many references can be found in the literature from the countries where infection with Taenia echinococcus is common showing an increased prevalence of the disease among the domesticated animals. Most of the known facts about