Chorionic villus sampling is now an acceptable alternative to second trimester amniocentesis. Several reports have raised concerns about the occurrence of discrepancies between the chorionic villi and fetal chromosomal constitution, which adds multiple diagnostic complexities to the process of prenatal genetic counselling. We report on a series of 26 cases in which fetoplacental discrepancies have occurred. The chromosomal aberration was exclusively con®ned to the placenta in 21 cases. Twice the identical aberration was also observed in amniotic ¯uid with variant range of aneuploidy. The chromosomal abnormality was found in amniotic ¯uid and fetal blood samples in two cases, and was absent in chorionic villi. One case had very unusual cytogenetic ®ndings as two different non-mosaic chromosomal abnormalities were identi®ed separately in the placenta and amniocytes. Among the 21 gestations with con®ned placental abnormal karyotype, three cases of intrauterine growth retardation were identi®ed. Of six cases evaluated for uniparental disomy, four demonstrated biparental inheritance. These ®ndings support a positive correlation between placental aneuploidy and abnormal fetal development. They also emphasize the importance of further DNA analysis whenever discrepant karyotype ®ndings between the placenta and amniocytes are identi®ed.