Balanced reciprocal translocations are the most common structural abnormalities; most involve two autosomes while a few involve a gonosome (X or Y chromosome) and an autosome. These rearrangements are usually associated with infertility and/or a higher risk of chromosomal imbalances among offspring. This 26 years old man was first seen because of a 3-year history of primary infertility. He had been found to have a translocation, t(X;18)(q11;p11.1), inherited from his mother when he was 9 years old. Semen analysis showed a very severe oligoasthenoteratozoospermia (OAT). A total of 447 spermatozoa were analysed using three-colour fluorescent in situ hybridization (FISH). The alternate segregation pattern, leading to a normal or balanced chromosomal content, was found in 54.36% of the spermatozoa studied. The frequencies of Adjacent I, Adjacent II, 3:1 segregation and diploidy (or 4:0 segregation) were 8.28, 5.14, 22.37 and 2.01%, respectively. Balanced reciprocal translocations between an autosome and the X chromosome lead to important disruptions in human spermatogenesis. Almost all the males with an X-autosome translocation have azoospermia. The man reported here had very severe OAT and is the first in whom the meiotic segregation pattern was analysed. This case further emphasizes the interest in performing FISH studies in infertile males with a chromosomal translocation to provide them with a personalized imbalance risk.