The aim of this retrospective study was to determine the pregnancy rate from the transfer of single genetically normal embryos in patients of advanced reproductive age. The study group included 23 patients (mean age 42.2 +/- 1.3 years) who underwent 27 in-vitro fertilization (IVF) cycles in which preimplantation genetic diagnosis (PGD) was carried out on single blastomeres from day 3 embryos. The control group included 54 patients (mean age 43.3 +/-1.9 years) who underwent 69 cycles of IVF without PGD. Ovarian stimulation in all patients consisted of follicular phase leuprolide acetate administration, followed by ovulation induction with gonadotrophins. The mean number of biopsied embryos was 5.6 +/- 0.5. No embryo transfer occurred in six patients (10 cycles) because all embryos biopsied were abnormal. Seventeen patients (17 cycles) each had one genetically normal embryo transferred resulting in six on-going clinical pregnancies (35% per embryo transfer cycle). The mean number of embryos transferred in the control group was 4.0 +/- 0.8. Nineteen clinical pregnancies were obtained in 69 transfer cycles in the control group (28% per embryo transfer cycle). The transfer of a single normal embryo in patients of advanced reproductive age can lead to acceptable pregnancy rates. Aneuploidy appears to be a major cause of reproductive failure in this group of patients.