Molecular analysis of Y-chromosomal microdeletions is routinely performed in the work-up of male infertility, in order to establish a diagnosis and for genetic counseling of the couple, since such microdeletions are transmitted to the male offspring. The review of published data shows that microdeletions are relatively common in patients with azoospermia or severe oligozoospermia, with wide variations in the reported deletion frequency depending mainly on the selection criteria. In general, patients with proximal deletions, involving the AZFa and/or the AZFb region show severe defects of spermatogenesis with a high prevalence of Sertoli cell only syndrome, while deletions of the distal AZFb and of the AZFc region can be compatible with residual spermatogenesis. Microdeletions have been only sporadically found in normozoospermic patients. For the time being the molecular analysis of microdeletions of the Y chromosome is indicated in infertile patients with sperm concentration <5 x 10(6)/ml and in men undergoing assisted reproduction techniques, since the genetic defect and, most probably, the related infertility problem will be transmitted to the sons.