Pulmonary histiocytosis X is rare granulomatous disorder of unknown etiology thar alters the interstitium of the lung. When confined to the lung, it is known as primary pulmonary histiocytosis X or eosinophilic granuloma of the lung. The chest radiograph shows characteristic nodular, reticular, and cystic abnormalities, which are most apparent in the upper and middle lung zones, but spare the costophrenic angles. The CT demonstrates innumerable small cysts with thin walls, and fine nodules. Recently we experienced pathologically proven primary pulmonary histiocystosis X in 35 yearas old male patient who had recurrent pneumothorax.