With recent advances in genetics, inherited disorders can now be diagnosed at a molecular level. For couples who are carriers or affected by any of these conditions and are at high risk for transmitting it to their offspring, it is currently possible to detect the disorder during pregnancy. However the couples have the dilemma of whether or not to terminate the pregnancy if the genetic abnormality is present. In some cases this may also not be a viable option for religious or moral reasons. An alternative would then be to diagnose the condition in embryos before the pregnancy is established. Only the unaffected embryos would then be transferred to the uterus. This technique is referred to as Preimplantation Genetic Diagnosis (PGD). PGD is, presently, a valid alternative for families at a high risk for producing offspring with genetic disorders and to those who wish to avoid elective pregnancy termination or to prevent the birth of an affected child following prenatal diagnosis. PGD allows genetic analysis to be performed on early embryos prior to implantation and pregnancy. This provides couples at risk the opportunity to know that any pregnancy they achieve should be unaffected and obviates the need for screening during a pregnancy and hence prevent the physical and psychological trauma, and ethical-moral problems associated with possible termination. Technical advances in molecular genetics now enable physicians and scientists to be able to diagnose some inherited genetic or chromosomal disorders from a single cell of an early embryo. The information gained by PGD is used to select for replacement in the uterus only those embryos considered unlikely to be affected by the specific genetic disorder for which testing is performed. Couples who have PGD will undergo an in vitro fertilization (IVF) cycle for the purpose of creating embryos from the woman's eggs and man's sperm which will have genetic testing prior to replacement into the woman's uterus. The genetic material of the embryos is not altered in any way during a PGD cycle, and early embryological development is similar to natural conception, except that it occurs in the laboratory. Embryos that show normal development are biopsied with micromanipulation techniques to obtain sufficient cells (blastomeres) for analysis. The cells removed from each individual embryo are analyzed by genetic testing using PCR-based DNA amplification. Those embryos considered to be unaffected on the basis of this testing will then be available to be transferred into the woman's uterus. At least 1500 PGD cycles have been performed for single gene disorders, resulting in births of more than 300 unaffected children. The list of disorders, presently comprising more than 50 different conditions, for which PGD has been applied is being extended beyond the indications for prenatal diagnosis, although the most frequent ones are still cystic fibrosis and haemoglobin disorders. The important present feature of PGD is its expansion to a variety of conditions, which have never been considered as an indication for prenatal diagnosis, including the late-onset disorders with genetic predisposition and preimplantation HLA matching. The six years experience of our Centre includes 250 PGD cycles for single gene disorders performed on embryos of 174 couples for 23 different genetic conditions. Overall 71 pregnancies were established, 15 of which resulted biochemical, 6 spontaneously miscarried, two resulted ectopic and were terminated, 9 are still ongoing. The remaining pregnancies were confirmed to be unaffected and went to term without complications, resulting in the birth of 35 healthy babies. It may be expected that PGD will soon be available for any inherited condition. PGD has opened up new possibilities for genetic research and has offered hope to couples that wish to have healthy children but are unwilling to undergo termination of pregnancy. Enhanced awareness of PGD and decreasing cost may lead to consider PGD as a valid alternative to prenatal diagnosis.