SummaryThe surgical anatomy of five types of intrathoracic complication of liver hydatid disease has been described.Seven case histories, illustrating the clinical picture and the surgical treatment of each type of hepato‐thoracic hydatid disease, are presented. Mr. John Hayward operated on Cases 2, 3 and 5, and I thank him for permission to include their clinical histories inthis series.If the subdiaphragmatic hydatid disease is adequately treated complicating lung abscesses and broncho‐biliary fistulae will heal. Definitive closure of a broncho‐biliary fistula is not indicated and drainage of a lung abscess or pulmonary resection will not be necessary.If pleural complications are present, both these and the liver hydatid require surgical treatment. The empyema contents must be evacuated, the lung and chest wall decorticated and the pleural cavity drained.A large hepato‐pulmonary hydatid cyst is best approached through a long thoraco‐abdominal incision. This exposure makes it more likely that all hydatid cysts will be removed, under vision, from the liver.After removal of the hydatid from the liver, the adventitia, if calcified, should be excised. Haemorrhage is usually severe; but it can usually be controlled. Excision of thecalcified adventitia decreases greatly the period of drainage from the liver cavity‐an infected, calcified liver cavity may drain forever. I am grateful to Mr. Fitzpatrick of Hamilton for suggesting an alternative method of dealing with a liver cavity with a calcified adventitial wall He suggests that the wall be swabbed and scraped, and the cavity closed by suture, and he advises against drainage of such cavities, even when obviously infected. In his extensive experience infection seldom recurs, and it is therefore rarely necessary to re‐operate to drain a liver cavity so treated. This method of treatment certainlyeliminates the possibility of a fatal haemorrhage from the liver during excision of the calcified adventitia.The coughing up of daughter cysts and the finding of daughter cysts in a lung hydatid at operation, usually mean that the patient is suffering from hepato‐thoracic hydatid disease. The liver hydatid should be sought and treated. It is realised that primary lung hydatids occasionally contain daughter cysts and that daughter cysts in a lung or pleural hydatid, which has developed because of spillage of hydatid elements due to a previous operation for lung hydatid, is fairly common.In Australia the commonest cause of the coughing up of bile is hepato‐pulmonar