We present a case a right-sided retroperitoneal lymphaticmalformation (LM), extending from the abdomen to the right thigh,without other abnormality, discovered at the second trimester scan.Fetal karyotype was 46, XY. After multidisciplinary counselling,parents chose for a termination of pregnancy. Pathology confirmedthe isolated malformation.LM are benign congenital malformations of the lymphaticsystem. Their prevalence is 1-5/10 000. Prenatal mortality rateis overall of 50-100%, for associated malformations and karyotypeabnormalities. Isolated LM can cause compression of adjacentorgans. 95% are localized in the head, neck and axillary region.Retroperitoneal LM account for 1% of cases. Few case reports existof isolated retroperitoneal LM. Limb affection is a typical featureof retroperitoneal LM. Most of them are left-sided, as opposed toour case. Pediatric complications are: hemorrhage, infection, massrupture or twist.Fetal ultrasound is a reliable diagnostic tool and can be completedby MRI. It assesses prognostic factors and can be used tomonitor tumor growth and fetal well-being. Main features arehypoechogenic, multicystic, multiseptated mass.Treatment of choice is surgery, with risk of resection of adjacentorgans, recidive and high morbidity and mortality. Sclerotherapycan be a useful adjuvant tool.Parental counselling must be multidisciplinary. Discussion onmode of delivery is mandatory, due to the high risk of dystocia. ; info:eu-repo/semantics/published