A one-week-old boy had undergone resection of a sacrococcygeal benign cystic teratoma. At the age of 12 months, he had a serum alpha-fetoprotein level of 139,000 IU/ml and a recurrent pelvic mass which was removed, and the microscopic examination revealed endodermal sinus tumor. Postoperatively, massively enlarged inguinal lymph nodes and abdominal distention developed. Computerized tomography displayed enlarged inguinal lymph nodes, metastatic lesions in the liver, and a pelvic recurrent mass. He received BEP (bleomycin, etoposide, cisplatin) chemotherapy regimen, and a complete remission was achieved with a normal serum alpha-fetoprotein. Close follow-up and serum alpha-fetoprotein monitoring are mandatory after the resection of a sacrococcygeal teratoma.