The authors present a case of a 14-year-old premenarchal girl with a large solid tumor of the left ovary. The rim of normal ovarian tissue was visible around the tumor on ultrasonography scan. Although the levels of two tumor markers, LDH and CA125, were elevated, the authors performed an organ-sparing tumorectomy. The final pathology report revealed foci of immature neural tissue, with a final diagnosis immature teratoma Stage Ia.