Ectopic immature renal tissue has rarely been reported in literature, associated or not with teratoma. Its finding could be matter of concern, owing to the occasional possibility that Wilms tumor may develop in this setting. We report a 1-year-old male patient who underwent surgery for a sacral subcutaneous small teratoma with a prevalent component of immature renal tissue. The lesion appeared completely excised and, in absence of features of malignancy, only follow-up was suggested. The patient was alive and well 15 months postoperatively. Whenever ectopic immature renal tissue is detected, a proper histological interpretation is mandatory, in order to plan a suitable treatment of the patient. From an extensive analysis of cases reported in literature we draw some practical suggestions for the diagnosis and treatment of this rare condition.
