Using current demographic projection of maternal age-structure, age-specific fertility rates, and the availability, detection and utilization rates of prenatal diagnosis and subsequent termination rates, predictions are made of the likely numbers of births witb Down's syndrome (DS) in England and Wales to be expected up to the year 2000. Further predictions are made of age-specific prevalence of the condition bearing in mind recent trends in stirvival. These figures show that, despite current screening policies based on maternal age alone, the observed live birth prevalence of DS will rise to levels higher tban bave been seen for 20 years. Together with consistently increased survival, this will mean that, throughout the next century, tbe population prevalence of DS will be higher than ever before. Work based in other countries has reached similar conclusions. As the prevention of all birtbs affected by DS is not possible in the forseeable future, and some would argue that it is not desirable, society will need to provide for those affected.