A left upper quadrant fetal abdominal mass was detected at 24 weeks gestation. The mass was again confirmed in a postnatal ultrasound. Pathological analysis of the excised mass demonstrated an intraabdominal lung sequestration with Stocker type II congenital cystic adenomatoid malformation (CCAM). The sonographic characteristic of these lesions are those of a homogeneous echogenic mass with variable shape passing through or arising from the diaphragm. Surgical excision is recommended because of the uncertainty of the preoperative diagnosis and the possibility of malignant changes in CCAM.