Polysomy 49,XXXXY is a rare sex chromosome aneuploidy syndrome characterized by mental retardation, severe speech impairment, craniofacial abnormalities, multiple skeletal defects and genital abnormalities. We describe a patient with 49,XXXXY syndrome who had many characteristics of Fraccaro syndrome; language impairment, mongoloid slant, epicanthal folds, cryptorchidism, umbilical hernia and dysmyelinization in his brain. A GTG-banding technique was used for karyotype analysis of peripheral blood cell cultures. The parental origin of polysomy X was identified by using quantitative fluorescent polymerase chain reaction (QF-PCR) with seven short tandem repeat (STR) markers specific for the X/Y-chromosome which revealed that all the X-chromosomes were of maternal origin. This report provides evidence for successive non disjunctions in maternal meiosis I and II.