A patient was referred for amniotic fluid cell culture because of advanced maternal age. A decisional dilemma presented itself as a result of the detection of a metacentric bisatellited microchromosome (47,XX + marker) in the amniotic fluid cell culture. The decision whether to terminate the pregnancy had to be considered because the literature revealed a number of cases of an extra marker in patients with single or multiple congenital abnormalities, although other patients with a similar marker were phenotypically completely normal. The finding of an identical marker chromosome in the phenotypically normal mother and two of her off-spring favoured the continuation of the pregnancy. It would appear as if this is the first reported case in which a familial marker chromosome was detected prenatally and the pregnancy permitted to continue to term with the birth of a normal infant.