Six cases are reported with discrepancies between the karyotypes of placental cells and cells from other fetal tissue. The respective findings were: 48, + 7, + 18 resp. 47, + 18. 46,i(18q) resp. 46,del18(p11). 46,XX resp. 46,XX/47,XXX. 46,X,Yq+ and 46,XY resp. 46,XY. 46/47, + 12 resp. 46. 46/47, + 5 resp. 46. These differences were found in both early and term pregnancies. Care should be taken in deducing the fetal karyotype from the chromosomal pattern of placental cells.