We have treated four prenatally diagnosed cases of extensive congenital cystic adenomatoid malformation (CCAM) of the lung. The first case in 1982 was associated with severe fetal hydrops. After thoracentesis at 31 weeks of gestation abruptio placentae occurred, and a female baby was delivered by cesarean section, She underwent a right lower lobectomy, but soon died, The second baby without hydrops, diagnosed as having CCAM at 26 weeks of gestation, was followed conservatively until full term. After birth, it was necessary to treat the baby boy with extracorporeal membrane oxygenation (ECMO), but he survived. The third baby with fetal hydrops had an indwelling drainage catheter inserted into the CCAM at 27 weeks of gestation. The hydrops subsided and the baby was delivered at 37 weeks of gestation. He was allowed to breathe spontaneously, but was intubated 16 hours after birth. A right lower lobectomy was successfully performed 24 hours after delivery. The fourth baby without fetal hydrops was followed conservatively until delivery. He underwent left lower lobectomy successfully on the 4th day of life. Although management of prenatally diagnosed CCAM varies among patients, insertion of an indwelling catheter into the cyst appears to be the treatment of choice if indicated; the catheter can be maintained for as long as 10 weeks, as shown in Case 3. Cases of CCAM without fetal hydrops should also be treated carefully, because persistent fetal circulation may occur postnatally.