The author report a case of enteroid retroperitoneal cyst treated by enucleation. Such a lesion raises mainly the problem of histological recognition and embryological interpretation for which there are two possible theories: (1) Uptake, before sealing off of the embryo, of a cell group of endoblastic origin which develops some distance from the digestive tract. (2) Retroperitoneal course of a simple teratoma of enteroid type. Such a possibility of teratoma leaves open the possibility of malignant transformation.