Preimplantation genetic diagnosis and some prenatal screening programmes have been criticized for being 'eugenic'. This paper aims to analyse this criticism and to evaluate one of the main ethical arguments lying behind it. It starts with a discussion of the meaning of the term 'eugenics' and of some relevant distinctions: for example, that between objections to eugenic ends and objections to certain means of achieving them. Next, a particular argument against using preimplantation genetic diagnosis to 'screen out' disability is considered, one based on the Equal Value Principle, which says that we should value disability and non-disability equally. It is argued that present practice and policy probably do violate the Equal Value Principle, but that this principle is itself unsound.