The development of intracytoplasmic sperm injection (ICSI) for treatment of infertility as a result of severe male factor has improved the chances of achieving pregnancy in many infertile couples. However, concerns have been raised regarding the safety of this technique, because natural sperm selection is bypassed. In the present study, 25 oligoasthenozoospermic patients who were divided into two groups according to age: group A, 20-34 (n = 10) and group B, 35-50 (n = 15), were included. Pooling the data of the three semen parameters that were tested (volume, concentration and progressive motility) no statistically significant difference between the two age groups was found. A total of 50 883 decondensed spermatozoa was analysed using the dual and triple colour fluorescence in situ hybridization to estimate the rates of aneuploidy for chromosomes 13, 18, 21, X and Y in the two age groups. There was a significantly higher incidence of disomy for chromosome 21 compared to the other autosomes (chromosomes 13 and 18) in both age groups. The disomy rate of XY was significantly higher in the younger subject group (0.1%) compared to the older group (0.05%, p < 0.05). Statistically significant differences in the mean number of clinical pregnancies and abortions were not observed between the two age groups. The aneuploidy rates for all the analysed chromosomes did not differ significantly, both between and within the two age groups, and as a result there seems to be no effect of male age on chromosome numbers in the spermatozoa and on the ICSI outcome.