A case of de novo mosaic partial trisomy of chromosome 5 (q33-q ter) in a stillborn male fetus with bilateral polycystic kidneys, and atrial septal defect, is reported. Fetal cord blood sampling was carried out at 25 weeks of gestation because of bilateral polycystic kidneys with severe oligohydramnios observed on ultrasound examination of the fetus. The family history was notable for the presence of similar phenotypic abnormality in the mother and sibling. However, no chromosomal abnormality was detected in other family members. Significance of this rare chromosomal abnormality and its association with congenital malformations in the fetus and in the family is being discussed.
