Computed tomography sacn results of a 16-year-old female patient revealed the presence of suspected immature teratoma and peritoneal seeding in the right ovary and laparoscopic right salpingo-oophorectomy and multiple biopsies of peritoneal masses were performed. A diagnosis of immature teratoma in the right ovary, associated with gliomatosis pertonei(GP) was made in biopsy results. Chemotherapy with bleomycin, etoposide, and cisplatin was administered 3 times, and a second-look operation was performed 3 months later. Preoperative tumor marker levels were normal. CT results revealed the presence of a diffuse, soft tissue enhancing lesion in the cul-de-sac and in the right paracolic gutter, a moderate amount of fluid in the cul- de-sac and a functional cyst in the left ovary. The laparoscopic findings revealed that the uterus appeared normal on visual inspection, a 3cm, hemorrhagic corpus-luteal cyst was observed in the left adnexa. The peritoneal mass that had progressed, as identified on CT scan, was nodular, cancerous, and thick and had diffused and densely spread out over the entire posterior cul-de-sac. Such a nodule was also found in the bladder peritoneum in an area of approximately 3×4 cm. Subsequently, these masses were via by peritonectomy, and frozen section biopsies showed benign findings. Nodules were spread throughout the peritoneum and peritoneal mass resection was performed in the right and left paracolic gutter, right upper quadrent abdomenl. Nodules were also spread out throughout the omentum, and resection was performed. Postoperative biopsy results revealed the presence of GP with foci of mature non-neural tissue, in all tissue samples. The results of ultrasound and CT scan performed 3 months after surgery revealed normal with no masses or ascites. CA-125 and AFP, when assessed 3 and 6 months later were within normal range. Follow-up measurements of tumor marker and imaging were scheduled at 3-month intervals.