A condition in which there are no sperm in the semen when a man ejaculates. This may be because the man does not make sperm or because the sperm is blocked from entering the semen. Azoospermia may be caused by hormone problems, certain genetic conditions, previous vasectomy or other surgery, or other conditions. It may also be caused by certain cancer treatments. Azoospermia can cause infertility (the inability to produce children).