Y chromosome microdeletion (YCM) is a family of genetic disorders caused by missing gene(s) in the Y chromosome. Many men with YCM exhibit no symptoms and lead normal lives. However, YCM is also known to be present in a significant number of men with reduced fertility. Men with reduced sperm production (in up to 20% of men with reduced sperm count, some form of YCM has been detected) varies from oligozoospermia, significant lack of sperm, or azoospermia, complete lack of sperm. Three different spermatogenesis loci have been mapped on the Y chromosome and named "azoospermia factors" (AZFa, b, and c). Deletions in these regions remove one or more of the candidate genes (DAZ, RBMY, USP9Y, and DBY) and cause severe testiculopathy leading to male infertility. Y chromosome microdeletion analysis should routinely be offered to all men with severe oligospermia or azoospermia.