Retroperitoneal teratoma is infrequent (5% of all teratomas). The diagnosis is usually made within the first year of life. Two cases are reported. Case n. 1 is typical of mature benign teratoma with teeth, fat and water densities visible on the plain film of the abdomen. Cases n. 2 a malignant partly ossified immature teratoma. The ossification is in continuity of a congenital block of vertebral bodies L2 and L3; this association has not been reported in the literature. CT in both cases was contributive for delineation of the tumor but did not help to answer the question of malignancy or not; foeto-protein remains the only test to do that discrimination.