We report the prenatal diagnosis of a fetus with a de novo Robertsonian 
translocation: 45,XY,der(15;15)(q10;q10). Although Robertsonian translocations 
are common chromosomal rearrangements, those involving homologous chromosomes 
are infrequent. Since chromosome 15 is imprinted, uniparental disomy (UPD) is a 
concern when chromosomal rearrangements involving chromosome 15 are identified. 
In the present case, UPD studies showed normal biparental inheritance. In 
contrast to the fact that most homologous acrocentric rearrangements are 
isochromosomes, these results indicate postzygotic formation of a Robertsonian 
translocation between biparentally inherited chromosomes 15.