We report a case of an early (22-week) prenatal diagnosis of type II congenital cystic adenomatoid malformation of the lung complicated by a mediastinal shift. Detailed ultrasound examination of the fetus, including fetal Doppler velocimetry and echocardiography, and diagnostic amniocentesis were normal. There was a gradual, spontaneous resolution of the mediastinal shift and improvement in the lung lesions. The intrapartum and early neonatal clinical courses were uneventful.