A 9-year-old male patient developed a germ cell tumor in the right basal ganglia which secreted beta-human chorionic gonadotropin (beta-HCG) and caused precocious puberty. Histology and immunohistochemical staining for placental alkaline phosphatase (PLAP), alpha-fetoprotein (alpha-FP), and beta-HCG showed a mixed population of neoplastic germinocytes, embryonal carcinoma, and syncytiotrophoblastic giant cells (STGC). Immunohistochemical double-staining for alpha-FP and beta-HCG revealed that these two markers were produced by different subsets of cells. Expression of the proliferation marker Ki-67 showed a growth fraction of 53% for the neoplastic germinocytes and embryonal carcinoma cells, but only 21% for the STGC.