ABSTRACT Objective To investigate the prenatal ultrasonography characteristics and prognosis of congenital cystic adenomatoid malformation (CCAM). Methods Forty-six fetuses of prenatally diagnosed CCAM using ultrasonography were retrospectively analyzed. The prenatal ultrasonographic features, thoracic indicators, presence or absence of mediastinal shifts, polyhydramnios, fetal edema or hydrops, complicated malformation , mass volume changes and prognosis at follow-up were analyzed. Results (1)Prenatal ultrasonography characteristics of CCAM: According to the size of cyst, the CCAM can be divided into large cystic type (type I, 9/46), medium cystic type (type II, 22/46) and micro cystic type (type III, 15/46). The lesions were located in unilateral thorax in 43 cases and bilateral thorax in 3 cases. The CCAM volume ratio (CVR), lung volume and thoracic volume ratio were gradually increased in different CCAM types (P<0.05), while there was no significant difference in mass volume, thoracic transverse diameter, anteroposterior diameter, area, chest circumference, lung volume and thoracic volume in different CCAM types (P > 0.05). (2) Complications of CCAM: The presence or absence of polyhydramnios, fetal edema, hydrops was different among different types, type III was more than type II, and type I was the least (P< 0.05), while there was no statistically significant difference in mediastinal shift, complicated malformation, and decreased mass size at follow-up (P > 0.05). (3) Prognosis of CCAM: The pregnancy outcomes were different in different types, type III was the worst (P＜0.05), while there was no statistically significant difference in postpartum intervention. The prognosis of fetuses complicating with hydrops were poor. Conclusion (1) Prenatal ultrasonography characteristics of CCAM is typical . The classification of CCAM is related to the size of cyst, CVR, lung volume and thoracic volume ratio. (2) The complications are different in different types of CCAM , prenatal ultrasound can evaluate the prognosis according to the types and complications, type III is worse than type I and type II.