This work aimed to determine the incidence of sperm disomy in infertile men with idiopathic severe oligoasthenoteratozoospermia (OAT). Fifty male subjects were included in this study: 30 infertile men with idiopathic severe OAT and 20 healthy fertile men as controls. Semen analysis, hormonal assay (follicle-stimulating hormone, luteinising hormone and testosterone), scrotal ultrasound examination and fluorescent in situ hybridisation of their semen samples were performed to determine the disomy levels of chromosomes X and Y. There was a significant higher frequency for XX disomy and XY disomy in spermatozoa from severe OAT patients than that in controls. There was nonsignificant difference in the percentage of YY disomy between OAT cases and controls. XX, YY and XY disomy showed nonsignificant correlation with the age. Sperm concentration and sperm motility demonstrated significant negative correlation with XX and XY disomy. Sperm abnormal forms had significant negative correlation with XX and XY disomy. Nonsignificant correlation was demonstrated between YY disomy and semen parameters. XX disomy showed significant positive correlation with XY disomy and nonsignificant correlation with YY disomy. YY disomy showed nonsignificant correlation with XY disomy. It is concluded that sperm disomy in severe OAT is increased, which should be taken into account when undergoing micromanipulation.