The development of assisted reproductive technologies, such as intracytoplasmic sperm injection (ICSI) substantially improved the outlook for patients with severe male fertility problems. However this implies that for the first time genetic defects associated with male in- or subfertility might be transmitted to offspring and result in genetic disease [de Kretser DM, The potential of intracytoplasmic sperm injection (ICSI) to transmit genetic defects causing male infertility. Reprod. Fertil. Dev. 1995;7:137-142]. The knowledge of male specific fertility genes on the Y chromosome increased enormously in the last decade. The SRY gene plays a critical role in gonadal differentiation. DAZ, SPGY and related genes on the Y chromosome are very important for spermatogenesis. Interstitial Y-chromosomal microdeletions encompassing the AZFa, b or c region have become an additional class of genetic abnormalities causing male infertility. A review is given of the different genetic aspects of male infertility.