Two cases of Swyer-James syndrome are reported. Case 1; A 25-year-old man was admitted to our hospital to be treated for Mycobacterium avium infection. Chest X-ray film revealed hyperlucency in the right lower lung. High-resolution CT showed a low attenuation area and bronchiectasis in the right lower lobe. He had had two episodes of pneumonia in his childhood. 3D CT scan showed a narrowing of right lower pulmonary arteries. Case 2; A 65-year-old woman was admitted to our hospital with dyspnea on effort. Chest X-ray film revealed hyperlucency in the right lung. Chest CT scan on inspiration and expiration detected air-trapping, which is characteristic of this syndrome. In both cases, the volume of the hyper lucent lung was normal. From these clinical findings, we diagnosed these two cases as Swyer-James syndrome and in this paper described the clinical features and treatment.