The authors report a case of neonatal neuroblastoma mimicking Altman type III sacrococcygeal teratoma. A newborn male infant delivered after a normal pregnancy was found to have an extremely large sacrococcygeal mass. Imaging studies strongly suggested Altman type III sacrococcygeal teratoma. On the 10th day after the birth, the tumor was incompletely removed at surgery. Histopathologic examination of the tumor showed neuroblastoma. The tumor disappeared completely after chemotherapy. One year after diagnosis, no local recurrence or metastasis had been detected. To the authors' knowledge, this is the first case of neonatal neuroblastoma mimicking Altman type III sacrococcygeal teratoma.