The A. report a cytogenetic study performed on 201 subjects with a defective reproductive fitness. In total, they detected 37 chromosomal changes (18.4%): 7 in 48 subjects (24 couples) with sterility (14.5%), 11 in 96 with hypogonadism and/or criptorchidism (11.4%), 15 in 38 women with oligoamenorrhoea (39.4%) and 4 in 4 patients with Morris syndrome (100%). On the contrary, no chromosomal change was detected in 15 patients with pure gynecomastia. The A. discuss the significance of these chromosomal aberrations, and particularly: the mosaicism XO/XX, because this chromosome picture may be associated with fertility, as in our case; the isodicentric X, because the patient showed the clinical features of the Turner's syndrome; the inv(11), because the patient showed a progressive oligoamenorrhoea, leading us to retain that some chromosome changes, by determining a severe gametic selection, may cause infertility in these subjects. the t(13;14), detected in men with azoospermia, because these changes confirm the presence of a gametic selection, mostly in men. Therefore, according to other reports, the A. suggest that the cytogenetic investigations should be performed in all subjects with abnormal reproductive fitness, for a more accurate diagnostic iter.