Preimplantation genetic diagnosis (PGD) is a very early form of genetic testing. It involves testing one or two cells taken from a recent embryo of eight cells produced by in vitro fertilization, and selective transfer of genetically normal embryos. So far in the Academic Hospital Maastricht, the Netherlands, 20 couples have undergone PGD, resulting in 6 ongoing pregnancies (one twin pregnancy). In three women the indications for PGD were: cystic fibrosis, sex-linked Pelizaeus-Merzbacher disease and chromosomal translocation, respectively. In the Netherlands PGD is only allowed if there is a high risk of a serious genetic disease. PGD can be carried out in Maastricht for: cystic fibrosis, sex-linked diseases, chromosomal abnormalities, fragile X syndrome, spinal muscular atrophy and myotonic dystrophy. The advantage of PGD is that it excludes the necessity of a therapeutic abortion. Disadvantages ages are the requirement of in vitro fertilization, which has only a 15-20% pregnancy rate, and the experimental nature of the PGD procedure. To date, about 200 children have been born worldwide following PGD.