Octamer4/3 is a POU transcription factor that regulates pluripotentiality in embryonic stem and germ cells and primordial germ cells. When expressed in post-embryonic life, Octamer4/3 may lead to malignant germ cell tumors (GCT). Thirty samples were selected for this study (26 GCT samples and 4 cryptorchid testes samples) and 16 non-GCT were used as controls. Samples were stained with an anti-Octamer4/3 antibody. All cases of GCT were positive for Octamer4/3, and the non-GCT were negative. This article focuses on pediatric populations where we found that Octamer4/3 immunostaining is a useful diagnostic tool in undifferentiated pediatric tumors.