The teratoma is a unique complex neoplasm and is one of the most frequent pediatric tumors originated from the extragonadal germ cells. Mature teratoma is composed of mature differentiated tissues, while immature teratoma always contains embryonic tissues of variable degrees of immaturity, especially in the neuroepithelial elements. Diagnosis of teratoma is relatively easy by conventional radiologic study, but the immaturity can be identified only by histopathological examination. Between January 1993 to December 2002, 63 cases of teratoma were operated and analysed retrospectively at the Chonnam University Hospital Female to male ratio was about 3:1 and age distribution was relatively even. Among 63 cases, gonadal teratoma was the most common (52.4%), followed by sacrococcygeal (25.4%), retroperitoneal (9.5%) and mediastinal teratoma (9.5%). Fifty-six cases were mature teratomas and seven were immature teratomas. Alpha-fetoprotein (AFP) was elevated in 4 of 6 immature cases, but in 2 of 51 mature ones Elevated AFP progressively returned to normal range by 1 month after operation in all. Complete excision of the mass was performed, and major complication was not noticed. In five immature cases, PEB chemotherapy (Cisplatin, Etoposide, Bleomycin) was performed. Two of 2 cases in histological grade II were well tolerated to the aggressive chemotherapy. One of three cases in grade III expired due to severe bone marrow depression, and two of them expired by tumor recurrences. In conclusion, immature teratoma in histological grade III showed high potentiality of recurrence. Therefore, postoperative chemotherapy has to be applied to the high graded immature tumors.