BACKGROUND Congenital cystic adenomatoid malformation (CCAM) is mostly reported from the second trimester of pregnancy. We report a case of a microcystic type of CCAM that was suggested by routine ultrasound examination at a gestational age of 12 weeks. CASE REPORT First-trimester ultrasound screening revealed the presence of a hyperechoic image that occupied the whole of the right lung, without no other any associated complications. The cardiac and aorta deviations with diaphragmatic eversion associated with a poly-hydramnios had subsequently appeared. The diagnosis of CCAM was confirmed histologically after termination of the pregnancy at 25 weeks of gestation. CONCLUSIONS CCAM may occur at a very early stage of fetal lung development.