We describe a female neonate with an oral teratoma showing bone, teeth, and epidermis, but also epididymal (male) tissue. PCR amplification of Y-chromosomal DNA clearly showed male DNA from paraffin-embedded tumour tissue. The girl had a normal female karyotype without abnormalities of the genital organs. There are at least three hypotheses for the origin of teratomas: parthenogenesis, incomplete twinning, and totipotent somatic-cell origin. This case supports the hypothesis of an included dizygotic twin, and might contribute to the elucidation of the pathogenesis of extragonadal teratomas.
