Background: Cystic lymphangioma is a rare benign malformative tumor of lymphatic vessels in various locations. The retroperitoneal localization is less common compared to mesenteric one. Its clinical presentation is polymorphic and its discovery on the occasion of a pregnancy has rarely been described. The diagnosis is evoked by imaging but requires histological confirmation. Surgery is the treatment of choice. Case report: 22-year-old female presented for pregnancy control. Her clinical examination and ultrasounds reveled a giant abdominal cyst fulling the entire abdomen and exposing the pregnant for miscarriage. Surgical removal under laparotomy was carried out and the patient ?s postoperative recovery was uneventful. The giant cyst was diagnosed as a retroperitoneal cystic lymphangioma. Conclusion: we are reporting this rare case to share our experience in its management. The complete surgical removal of the cyst is possible even if it seems to encase major vessels as a clean plane of dissection usually exists.