A 3-year and 11-months-old boy presented with a 9-month history of increasing penile enlargement, pubic hair, deepening of the voice, and rapid growth. The erect penile length was 14 cm with bilateral testicular volume of 3 mL. Laboratory evaluation revealed suppressed follicle-stimulating hormone and luteinizing hormone, elevated total testosterone (259 ng/dL), elevated alpha feto-protein (AFP 79 ng/mL), rapidly increasing β-human chorionic gonadotropin (β-hCG 14-399 mIU/mL) over 2 weeks, and a karyotype revealed 47, XYY. Radiographic evaluation revealed a 1.5-cm mixed solid/cystic mass in the pineal gland. Chemotherapy was initiated to attempt to normalize the tumor markers (AFP and β-hCG). This is the first report of a nongerminomatous germ cell tumor (NGGCT) in a 47, XYY karyotype male. Tumor markers (hCG and AFP) should be included in the workup of adult males with 47, XYY as they are in children with precocious puberty.