We describe the case of a pregnant mother and her fetus who both carried teratomas during the pregnancy. The fetus was diagnosed at 38 weeks' gestation to have an intracranial mass, which was later determined to be an immature teratoma. During a cesarean section delivery, an ovarian tumor was found in the 27-year-old mother that was also diagnosed to be an immature teratoma. Because of the similar histology of the tumors carried by both mother and child, a single clonal origin was suspected. Using polymerase chain reaction (PCR) and electrophoresis of highly polymorphic DNA satellite sequences, we determined that the origin of the intracranial teratoma carried by the child was independent of the mother's tumor. We also examined the p53 tumor suppressor gene in constitutional cells from both mother and child for the possible presence of a cancer-predisposing inherited mutation, but none was found. To our knowledge, this is the first report of the simultaneous occurrence of independent malignant immature teratomas in a mother and child during pregnancy.