Three-color fluorescence in situ hybridization (FISH) was used to detect numerical X, Y, and 17 chromosomal aberrations in human sperm nuclei. Digoxigeninlabeled alpha satellite chromosome X-specific probe DXZ1, biotin-labeled classical satellite chromosome Y-specific probe DYZ1, and biotin plus digoxigenin-labeled alpha satellite chromosome 17-specific probe D17Z1 were simultaneously hybridized to sperm preparations from donors with normal semen (group A) and abnormal semen (group B) characteristics. The proportions of haploid X, Y, 17 and disomy, diploidy of them before and after swim-up were determined. At least 3,000 sperm were analyzed for each sample. Overall, up to 98% of sperm were labeled with the probes, and all statistical analyses were performed using chi 2 tests. A significant difference was observed between group A and group B in frequency of sex chromosome disomy (p < 0.05). In group B, there were significant differences in frequencies of sex chromosomes disomy (p < 0.05) and diploidy (p < 0.01) before to after swim-up. There was no significant difference in frequency of disomy 17 between the 2 groups. In group A and B, the ratios of X- to Y-bearing sperm were 1:1 (neat semen), but in both groups there was a significant increase in Y-bearing sperm after swim-up. The results of this study demonstrated that abnormal semen has sex chromosome disomy more frequently than does normal semen and that portion of sex chromosome disomic and diploid sperm is removed by swim-up, especially for abnormal semen. These findings suggest that we should be careful in using abnormal semen for IVF, especially for ICSI, and should perform swim-up if possible.