DESPITE a rapidly growing literature on cysts of the lung, there still exists a considerable disparity of opinion with reference to their genesis, diagnosis and mode of treatment. A recent monograph1 stated: Congenital cystic disease: Anatomic studies indicate that this is an extremely rare condition. It has not been found at necropsy at The Babies Hospital during a period of fifty years. Schenck quotes Lederer as having failed to find a single instance of congenital cystic disease in five thousand necropsies. It is now evident that many cases which have suggested congenital cysts roentgenographically were probably examples of acquired emphysematous cavities caused by check-valvular bronchial obstruction. The present cases of cystic disease of the lung in infants and children exemplify most types of cystic disease of the lung seen and present a fair sample of the types of accompanying anatomic anomalies (fig. 1). Ten of the 12 patients have