The condition named in the title of this article is uncommon and has attracted but little attention. It is a congenital deformity of the lung which may result in grave recurrent attacks of dyspnea and cyanosis in quite early life. The distressing attacks are apparently due to spontaneous rupture of the deformed lung with consequent positive pressure pneumothorax, and may prove fatal. The developmental anomaly of the lung may thus be the indirect cause of death, and although radical surgical measures are hardly to be considered in its management, nevertheless knowledge of the condition and its possible consequences is of interest to the thoracic surgeon. Congenital cystic lung was first brought to my attention by the following case: REPORT OF CASE An apparently healthy child, born spontaneously at term, was brought to the pediatric clinic of the Johns Hopkins Hospital when she was 5 weeks old with the statement that