Congenital immature teratoma of the tongue is a very rare form of extragonadal teratoma. We report an infant autopsy case of a huge congenital immature teratoma protruding from the tongue of a female infant born to a woman at 28 weeks' gestation of her first pregnancy. The mass obstructed the infant's mouth and produced hydroamnios. Maternal α-fetoprotein serum level was elevated and the infant's tumor was identified before birth by ultrasonography. The pregnancy was terminated by cesarean section. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:741-5)