Cystic lymphangioma of the retroperitoneum is a primary mesodermal derived benign neoplasm, arising from retroperitoneal lymphatics. The Authors report a case of cystic lymphangioma of the retroperitoneum recently observed, and a review of the international literature registering 181 cases from 1958 up to nowadays. Retroperitoneal localization, sub-clinic evolution and the impossibility to preoperatively define the histological type of the tumour, in spite of the modern diagnostic techniques, explain the difficulties to reach a correct differential diagnosis. The authors conclude that surgery only allows to exactly localize the tumour, yet the definition of cystic lymphangioma is an histological goal.