Gliomatosis peritonei (GP) is a rare occurrence associated exclusively with ovarian teratoma (OT), in which numerous metastatic nodules composed mainly of mature glial tissue are studded on the peritoneum, omentum, and bowel wall. Two female patients (aged 5 years and 14 years) are reported. Various preoperative examinations confirmed a large abdominal teratoma with normal alpha-fetoprotein and beta-HCG. The OT was excised and partial omentectomy and incidental appendectomy were performed to remove as many metastatic nodules as possible. Pathological examinations including immunostains for glial fibrillary acidic protein showed predominantly mature glial tissue in the OT and in the metastatic nodules. An addition, chemotherapy was given to one of them, but both were well without recurrent diseases 17 months and 12 months postoperatively, respectively. The outcome of these two cases, in contrast to advanced malignancy in widespread intraperitoneal metastases of any other kind, supports the concept of benign nature of GP and a conservative surgical approach to this rare disorder.