We present a database and a review of published literature on discrepancies in chorionic villus (CV) diagnostic findings. The review includes 457 cases of discrepancies between CV findings (direct, culture, or both) and the fetus. One hundred and one cases reported normal by CV direct harvest included 30 with abnormal or mosaic abnormal fetal karyotype (30% false negatives). The corresponding number of false negatives for CV culture was only 4 cases out of 133 (3%). Assuming no bias in reporting cases based on site of discrepancy (assumption may not hold), these data imply that the probability of false-negative findings is 10-fold higher by CV direct method compared to CV culture method. We also reviewed recent studies reporting on large series of CV diagnosis. This review revealed that the reported overall frequencies of discrepancies as a percentage of abnormal and mosaic abnormal CV results ranged from 11 to 63% (a mean of 37%). These data, together with recent reports of survival of embryos with reported abnormal karyotypes because of confined placental mosaicism (CPM), raise several questions pertaining to the predictive value of CV sampling and the origin of the discrepancies in the fetal-placental unit. Caution is recommended in counseling patients undergoing CV sampling to provide appropriate follow-up studies in cases of possible discrepancies.