Developmental pulmonary abnormalities are known as rare condition. diagnosis was made at autopsy in the early cases reported, however, as diagnostic aids such as X-ray, bronchography, bronchoscopy and exploratory thoracotomy have come into use, the condition is being discovered more often recently in living persons, and it appears to occur with sufficient frequency to merit consideration in the differential diagnosis of certain chest conditions. According to Schneider and Boyden there are three main types of this abnormality: [1] Agenesis, in which there is complete absence of one or both lungs; there is no trace of bronchial or vascular supply or of parenchymal tissue. [2] Aplasia, in which there is suppression of all but a rudimentary bronchus which ends in a blind pouch; there are no vessels or parenchyma. [3] Hypoplasia, in which the bronchus is fully formed but is reduced in size and ends in a _ flesh structure which usually lies within the mediastinum. Rudimentary pulmonary parenchyma may be present around the bronchial stump and often is the site of cystic malformation. We experienced one case of hypoplastic lung with cystic malformation which was originated from a small aberrant rudimentary bronchus, and the rudimentary bronchus was branched from the right side of tracheal end. The diagnosis was finally confirmed by the histopathological finding. Now, we report this case with a brief review of literatures.[KTCS 1975;1:13-18]