INTRODUCTION: It is common in infertile couples that the female partner age > or = 35 years, that some of them require assisted reproductive technology (ART) for their treatment, it is also well known that in this female age group increases the chance of chromosome aneuploidy in offsprings. It is known that the antenatal diagnosis may have the ethical dilemma and psychological impact. Therefore, the preimplantation genetic screening (PGS) may have a role in this ART group. OBJECTIVE: The present study had the objective to compare the incidence of normal, abnormal embryos and also aneuploidy of each chromosome, i.e. 13, 18, 21, X and Y between 2 subgroups of age i.e. the age 35-39 years and 32-39 years vs. the age > or = 40 years in both female and male partners respectively. MATERIALS AND METHOD: This prospective study was performed in 20 infertile couples attending the Fertility Clinic at Thammasat University Hospital during the years 2006-2007 of which the female partner aged > or = 35 years had to use the ART. The PGS was performed by FISH technique with 5 probes to detect the 13, 18, 21, X and Y chromosomes. The comparative analysis was made between 2 subgroups of both female and male partner aged, as mentioned above in the incidence of normal, abnormal embryos and aneuploidy of each chromosome by Chi-square test and Fisher's exact test with statistical significance if p < 0.05. RESULTS: The abnormal embryos in the female partner age > or = 40 years were higher than those of the age 35-39 years (72.4% vs. 52.5%, p = 0.07) but with no statistical significance. No different results were obtained in the comparable male partner age groups (56.8% vs. 61.4%, p = 0.66). The normal female and male embryos in the female partner age 40 years were lower than those of the age 35-39 years (10.4% vs. 25.4%, p = 0.08 and 17.2% vs. 22.1%, p = 0.60 respectively) but with no statistical significance. The normal female and male embryos in the male partner age > or = 40 years and the age 32-39 years were also compared with no significant differences (20.5% vs. 20.5%, p = 1.00 and 22.7% vs. 18.2%, p = 0.60, respectively). The percentage of embryos with aneuploidy of chromosome 18 in the female partner age > or = 40 years was significantly higher than that of the age 35-39 years (72.0% vs. 45.0%, p = 0.003). The pregnancy rate in the presented PGS study was 12.5% but unfortunately was associated with a high abortion rate of 100%. CONCLUSION: It was found in the present study that the incidence of abnormal embryos trend to increase in the female partner aged > or = 40 years compared to the aged 35-39 years although with no statistical significance. However, the incidence of embryos with aneuploidy of chromosome 18 was higher in females aged > or = 40 years with statistical significance, whereas the male partner age had no impact on the abnormality or normality of the embryo. The abortion rate was very high (100%) probably may be due to inadequate choice of probes, inappropriate fixation technology and small sample size. However, the results obtained in this study indicate that the PGS should be considerably performed with strong indication only.