Abstract
In a case of complete hydatidiform mole with fetus the genetic origins were defined by the use of chromosomal polymorphisms. The fetus had a normal 46,XY karyotype with evidence of the presence of both maternal and paternal chromosomes. The mole was 46,XX and of androgenetic origin. There was no evidence of a maternal contribution, and duplication of paternal chromosomes was shown. In such atypical molar pregnancies examining genetic polymorphisms yields much more information than do sex chromosome studies and karyotyping, particularly in confirming the diagnosis and defining the origin and aetiology of the condition.