The aim of this study was to determine whether sperm morphology and nuclear maturity are associated with an increase in the prevalence of disomy in human spermatozoa. Semen samples were obtained from 60 patients selected at random from a population of men undergoing semen analysis as part of consultation for infertility. Semen analysis and aniline blue staining were carried out on each ejaculate to assess nuclear maturity. Disomy frequencies were determined using 15-18 dual colour and X-Y-8 multicolour fluorescence in situ hybridization on the four groups of samples with the five lowest and the five highest teratozoospermia values (groups 1 and 2), and the five lowest and the five highest percentages of aniline blue staining (groups 3 and 4). The prevalence of autosomal disomy was significantly higher in group 4 compared with group 3, but differences between groups 1 and 2 were not significant. No significant differences in the prevalence of gonosomal disomies or diploidies were observed among the groups. These results indicate a link between chromosomal meiotic segregation and the dynamic process of nucleoproteins during gametogenesis. The difference observed between the frequency of autosomal and gonosomal disomy using aniline blue staining was unexpected and may be due to the extended isolation of the gonosomes in the heterochromatic body.