Endodermal sinus tumor (yolk sac tumor) is a highly malignant germ cell neoplasm which usually arises in the gonads. It is rare in the extragonadal regions including pineal, mediastinum, retroperitoneum, and sacrococcygeus. It affects mainly children and young adults. We report a case of primary retroperitoneal yolk sac tumor on angiographic study, CT imaging and histologic finding. The diagnosis can be made more precisely with evidence of elevated serum alpha fetoprotein as well as its characteristic images.