OBJECTIVES Abdominal cysts are seldom detected at the first trimester scan. The aim of this study is to ascertain their outcome, which is currently not established. METHODS The French College of Fetal Ultrasound conducted a prospective observational study of 24months, collecting all cases of abdominal cysts discovered during the first trimester ultrasound. Cases of megacystis were excluded from the study. Ultrasound images, prenatal diagnosis expert reports and pregnancy outcomes were collected by sonographers after patient consent. RESULTS Ten cases of abdominal cysts were collected. The cysts had a mean diameter of 15mm. They were anechoic in 5 cases, hyperechoic in 2 cases and mixed in 3 cases. In 6 of 10 cases, complete resolution was observed at 18WG with a good post-natal outcome; the five cases with anechoic images were associated with normal pediatric examination at birth and in the case of the resolved hyperechoic image, an isolated imperforate anus was observed. In the four cases of hyperechoic or mixed images that had not resolved, the outcome was poor with four termination of pregnancies, including two cases of cloacal dysgenesis. CONCLUSIONS Abdominal cysts are rare at the first trimester scan. They resolve in two thirds of cases and are then associated with good outcome. When they do not resolve or when they are not strictly anechoic, they require a referral ultrasound examination at 18 and 22WG.