We successfully performed shunting for a fetus with a multilocular macrocystic lung mass with hydrops at 22 weeks' gestation. Complete resolution of hydrops was achieved; however, at 35 weeks' gestation, the fetus developed acute massive pleural effusion. Fetal ultrasound examination revealed that one end of the shunting tube had migrated downward in the thoracic cavity, which led to fluid draining from the lung cyst. The baby was delivered at term and was discharged following neonatal intensive care management. Intrathoracic displacement of the shunt can occur, followed by massive pleural effusion due to drainage of cystic fluid.