A sacrococcygeal teratoma (SCT) is a neoplasm arising from the caudal end of the spine, usually protruding from the inferior end of the infant’s spinal column and displacing the anus forward. These tumors have a female-to-male ratio of at least 3:1.1 9 The incidence is approximately 1 in 40,000 live births,10 , 11 although a recent article from Finland12 found a prevalence of 1:14,900 in a study that ascertained the prevalence in the total population, including terminations of pregnancies and stillbirths. There is general agreement that SCT is the result of continued multiplication of totipotent cells from Hensen’s node that fail to apoptose at the end of embryonic life.7 , 13 , 14 This concept has received support from the work of Busch et al.,15 who have identified histochemical markers in SCTs supporting an origin from caudal embryonic stem cells. This provides convincing evidence against the theory that these tumors arise from migrating germ cells travelling from yolk sac to gonad. Economou et al.16 recently reported a series of experiments in mice exploring the results of injecting pluripotent cells into early embryos. They found that expression of Oct4 and Nanog in the primitive streak/tail bud after the start of somitogenesis does not result in neoplasia. Most authorities reject the concept that these are suppressed twins or parasitic fetuses. In 1976, Pantoja and Rodriguez-Ibanez17 reviewed the conflicting theories as to the origin of these tumors. Their findings still stand. Clearly, more studies are needed to determine the genetic influences that are associated with the formation of SCTs.