Hydatid disease is a parasitic infestation caused by the larval stage of the tapeworm genus Echinococcus. Inman, the two main forms are due to E. granulosus and, less frequently, E. multilocularis. Man becomes infected bycontact with definite host or by consuming contaminated water or vagetable. Hydatid disease is prevalentthroughout much of the world such as th emiddle east, eastern Australia, cental Europe, south America, Alaska, butit is very rare in Korea. We experienced one case of pulmonary hydatid disease. Chest films revealed ovoid mass inthe left lower lobe and seen as unilocular water-density cystic lesion on chest CT. which was removed surgically,and then the pathology confirmed the diagnosis.