Pre-natal-diagnosis technologies allow parents to discover whether their child is likely to suffer from serious disability. One argument for state funding of access to such technologies is that doing so would be "cost-effective", in the sense that the expected financial costs of such a programme would be outweighed by expected "benefits", stemming from the births of fewer children with serious disabilities. This argument is extremely controversial. This paper argues that the argument may not be as unacceptable as is often assumed. In doing so, it sets out a more general framework for assessing the relevance of efficiency calculations to policy-making. The final section also investigates the relationship between the paper’s arguments and claims about parental responsibility for child-bearing and rearing, with reference to Scanlon’s work on "substantive responsibility".