The immaturity of teratomas is usually manifested as immature neuroepithelium. The amount of immature neuroepithelium has been correlated with the survival of adult patients with ovarian immature teratoma. To date, no immunohistochemical marker has been found to facilitate the identification of immature teratoma. In this study, we evaluated the expression of glial cell line-derived neurotropic factor receptor alpha-1 (GFRalpha-1) for this purpose. We retrieved 38 cases of germ cell tumors: 26 cases contained immature teratoma, of which 24 had immature neuroepithelium and showed strong membrane staining for GFRalpha-1. No significant staining was seen in other components including embryonal carcinoma, seminoma, yolk sac tumor, choriocarcinoma, immature mesenchyme, and intratubular germ cell neoplasia. Immunohistochemical staining for GFRalpha-1 in immature neuroepithelium may facilitate its identification.