Preimplantation genetic diagnosis (PGD) purpose is to assess the genetic status of 3 day-old embryos. Thus, PGD offers to couples "at-risk" of transmitting a genetic disorder an earlier option to prenatal diagnosis. The first successful PGD was reported in 1990 but in France, PGD has been authorized only since 2000. Worldwide, 7,000 PGD have been performed, leading to the birth of more than one hundred unaffected children. New applications are introduced regularly and the number of diagnoses available is increasing at a rapid rate. In France the practice of PGD is strictly supervised by the bioethical law. However, indications vary considerably in countries where the absence of law authorizes all the practices, raising sometimes serious ethical issues.