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. PGD of single gene disorders, combined with HLA matching, represents one of the most recent applications in reproductive medicine. This strategy has emerged as a tool for couples at risk of transmitting a genetic disease to select unaffected embryos of a Human Leukocyte Antigen (HLA) tissue type compatible with that of an existing affected child. At delivering, stem cells from the newborn umbilical cord blood can be used to treat the affected sibling. Allogeneic haematopoietic stem cell (HSC) transplantation represents the only curative option for severe cases of haematopoietic disorders, including ß-thalassemia that has been recently classified as a public health problem. The best possibilities of cure are provided by transplantation with HLA-identical donors (~90% in patients with Pesaro low risk score).In fact, transplantation using donors other than HLA-identical siblings is less favourable compared with that with an HLA-identical donor, because associated with higher morbidity and poorer survival. Unfortunately, this cannot be applied in the majority of cases because of the difficulty to find HLA-matched donors, even among family members. Umbilical cord blood from HLA-identical siblings has been reported as an excellent source of stem cells. Moreover, the outcome after allogeneic HSC transplantation with HLA-identical stem cells obtained from umbilical cord seems to be comparable with bone marrow transplantation. Therefore, an increasing number of couples with a child affected by such a disease are requesting preimplantation HLA matching to conceive a healthy child who would became a future donor of HSC, to provide radical treatment for the existing affected recipient sibling. 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.