One third of the reproductive failure with genetic aetiology are explained by chromosomal rearrangements; the purpose of the study was to find the frequency of sex chromosome anomalies in Mexican population with amenorrhea, sterility or infertility at the National Institute of Perinatology. We realized cytogenetic studies at the Genetics' laboratory in blood samples from 1st january 1984 to 31st December 1995, with the next indications: amenorrhea, sterility, infertility and history of congenital defects that suggest chromosomal anomalies and correlated with the clinical findings. From 3,201 cytogenetic studies we performed in peripheral blood samples, we detected: 61 patients with anomalies of the sex chromosomes predominantly mosaics. We found sex chromosome rearrangements in 1.5% of the patients studied, so it's important to consider this aetiology in the study of infertility and sterility.