Most fetuses and babies with an extra sex chromo some are not identified1 because there are usually no indications for karyotyping.2–6 However, a sex chromo some anomaly is sometimes detected prenatally when amniocentesis is performed to exclude Down’s syndrome or other serious chromosomal anomalies. Conditions in which there is an extra sex chromosome are fundamentally different from those such as Down’s syndrome in which affected individuals have recognizable characteristics that can be explained by laboratory findings. Prenatal detection of sex chromo some anomalies and other karyotypes or genotypes that may have no phenotypic consequences or only mild ones will become more common as testing becomes more widely available.7 Understanding the difficulties faced by health professionals in disclosing the prenatal diagnosis of a sex chromosome anomaly can highlight some of the problems that may be encountered during the prenatal detection of other atypical laboratory findings in fetuses with phenotypes that are likely to fall within the normal range (table 1). We investigated how the prenatal diagnosis of a sex chromosome anomaly is first communicated to parents. We did not test a hypothesis but hoped to generate discussion about this issue. The first communication to parents is important because it may affect how information presented later is interpreted or even whether it is sought. Previous studies have looked at counseling that occurred once clinical geneticists.