Immature teratoma accounts for less than I percent of all ovarian teratomas and occurs commonly in young individuals, the peak incidence being in the second decade. It contains a variable mixture of mature and immature tissues in which neuroectodermal elements almost always predominate. Gliomatosis peritonei, miliary implants of mature glial tissues on the peritoneum or omentum, is an infrequently reported complication of mature or immature ovarian teratomas. We describe the first case in Korea of a 12-year-old girl with an immature teratoma and numerous glial peritoneal implants.