Azoospermia due to sperm production problems
Men who fail to produce sperm in the first place have this problem either due to a lack of certain hormones that are necessary to create sperm (pituitary hormones), so-called testicular failure, or a varicocele. The first category has the largest chance of successfully curing their azoospermia. Sometimes, taking hormonal medications is enough to cure this issue. Testicular failure can be caused genetically. A varicocele refers to dilated and swollen veins in the scrotum, or in other words excess blood that is not able to exit the scrotum. This is something that can often be corrected surgically.
Azoospermnia due to sperm delivery problems
Sperm delivery is the road sperm normally takes from the scrotum to the penis, where it leaves the body. Men who have sperm delivery issues produce sperm, but it is unable to leave their body for various reasons. These can include a complete lack of the vas deferens (the tubes that carry sperm from the testicles to the penis), a blockage of this tube, or a prior vasectomy (look at vasectomy pros and cons for more information). Ejaculatory problems also fall into this category. As you can see, a sperm count of zero can be caused by many different things. Some of the causes of azoospermnia can be corrected surgically, others medicinally. In some cases, men who produce sperm but have delivery failure can have it extracted directly from the testicles. These men can then have biological children with the help of ICSI, an IVF procedure where a single sperm is directly injected into an egg (see who benefits from intracytoplastic sperm injection?). Many men with azoospermnia can go on to have biological children, though they will need some assistance.