A case of idiopathic unilateral hyperlucent lung of a 25 years old male is presented in detail with some review on literatures. He had had symptoms referable to chronic bronchitis for several years, but family history was not contributory. Physical examination revealed limited respiratory movement of the left thoracic cage with scattered moist and dry rales on the same side. Roentgenograms of the chest revealed hyperlucency and decreased bronchovascular markings in the left lung. The mediastinum shifted to the left on inspiration and was restored to normal position on expiration. Bronchograms demonstrated cystic bronchiectasis and "pruned tree" appearance in the left lung. Pulmonary angiograms demonstrated non-visualization of the left pulmonary arterial tree except to the lingular segment, and perfusion lung scan using macroaggregated serum albumin-I131 (MAA-I131) showed markedly decreased radioactivity on the same areas of the left lung. Pulmonary function test disclosed markedly decreased vital capacity, maximal breathing capacity and severely restricted timed vital capacity. The symptoms disappeared after conservative treatment, but the hyperlucency of the left lung persisted on roentgenograms taken after one year.