Pulmonary hydatidosis is more frequently encountered in children than in adults. Chemotherapy with oral administration of particular antihelminthic agents (mebendazole and albendazole) has proved to be effective. This treatment, however, may be associated with serious complications that require surgical management. The aim of this study was to define the limitations of medical treatment, the subsequent complications, and their management. During a 16-year period (1985-2001), 36 children with pulmonary hydatidosis (Echinococcus cysticus) were medically treated. Oral antihelminthic agents (mebendazole until 1992 and albendazole thereafter) were given to all these patients. During this treatment, 11 patients developed complications requiring surgical intervention. In seven children, pleural empyema, or the presence of inflammatory residual fluid, was noted. The remaining four developed pulmonary abscess combined with fluid collection within the pleural cavity. In all complicated cases, the mean size of the cysts exceeded 6 cm in diameter at the beginning of medical treatment. At operation, suturing of communicating bronchi was insecure due to inflammation. Postoperatively, three patients had air leakage from the bronchial tree, requiring continuous suction and prolonged hospitalization. One patient presented with pneumothorax 4 months postoperatively and was operated on again. Overall, long-term results were good. We concluded that a) large pulmonary hydatid cysts should not be treated medically, b) incomplete expectoration of the cyst contents after the parasite death may lead to infection through bronchial communication, and c) patients surgically treated for complications following medical treatment are hospitalized twice as long as patients surgically treated in the first place.