A total of 150 infertile couples underwent chromosome analysis and genetic counselling before intracytoplasmic sperm injection (ICSI). Chromosomal abnormalities, including low-level sex chromosome mosaicism, were detected in 12% of the men and an unexpectedly high 6% of the women. Chromosomal abnormalities included gonosomal mosaicism in 13 cases, Robertsonian translocations in four males, autosomal reciprocal translocations in five cases, reciprocal translocation involving a sex chromosome in one case, inversions in three cases and a marker chromosome in one male. Chromosomal variants found in 11 women and 13 men were not included in the above percentages. Couples with a chromosomal aberration in one partner received a second counselling. The different aspects of genetic counselling in these couples are discussed. In conclusion, we recommend genetic counselling and chromosomal analysis of men and women prior to ICSI therapy.