Preimplantation genetic diagnosis for aneuploidy was implemented on 1782 morphologically normal embryos generated in vitro by patients with a poor prognosis of pregnancy. Only 592 of them (34%) were diagnosed as chromosomally normal. Embryo transfer was accomplished in 240 cycles resulting in 79 clinical pregnancies (33%) and an implantation rate of 22.6%. The in vitro efficiency of the procedure was established by analysing all the blastomeres obtained from 311 non transferrable embryos and resulted to be 97.1%. The in vivo efficiency of the technique was calculated with the data derived from the prenatal diagnoses by examination of the infants at birth and was 97.8%. In consideration of the reported inaccuracy rate, patients are still recommended to undergo prenatal diagnosis. The transfer of PGD selected embryos in women of advanced reproductive age reduces by half the risk of having a trisomic pregnancy.