AbstractThe effects of prenatal diagnosis on the birth frequency of Down syndrome are considered through a review of recent literature. Both present and possible future effects are discussed and brief mention of some psychological aspects of prenatal diagnosis is made. The incomplete uptake of amniocentesis is noted; ranging from 20% to over 40% of eligible women in recent British studies; reasons for this are explored. A consideration of reported changes in age specific incidence and their relationship to the introduction and continued use of prenatal diagnosis is given. Reductions in incidence of between 5% and 18% have been reported in the past. The maximum future effects, as predicted by studies using age in conjunction with biochemical screening methods, are noted; detection of up to 60% of affected foetuses is theoretically possible. However, problems of introducing this type of scheme may prevent such effective screening methods being widely adopted. This being the case, it seems unlikely that more than 15% of births affected by Down syndrome will be prevented by prenatal diagnosis in the foreseeable future.