Teratomas arising from totipotential primitive germ cell are composed of 2 or 3 germ cell layers. We reviewed the records of 166 children who underwent the operation for teratoma from Jan, 1990 through April, 2007. There were 40 boys and 126 girls (average age 6.93±5.83 years). Primary sites were ovary (n=88), sacrococcygeum (n=24), testis (n=16), retroperitoneum (n=16), mediastinum (n=8), brain (n=4), thymus (n=3) and a single tumor involved the adrenal gland, neck, middle ear, oropharynx, stomach, pelvis, omentum, chest wall and scalp. Teratomas were mature in 141 patients, and immature in 25. Six patients who had ovarian immature teratomas grade 2 or 3 with peritoneal gliomatosis underwent adjuvant chemotherapy. During follow up period, 6 mature teratomas recurred at sacrococcygeal area (n=1) and contralateral ovary (n=5). Five patients of them underwent reoperation and diagnosed as a mature teratoma, but one who had underwent a left salpingooophrectomy with right ovary cystectomy at initial operation was observed carefully. Teratomas were dominant in female patients and developed at various organs. Complete excision was needed for good prognosis. In case of immature teratoma, complete excision and appropriate chemotherapy according to grading can contribute to favorable results.