This is called Azoospermia.
There are 3 reasons for azoospermia
If the FSH hormone level is high then this indicates testicular failure and the testis has stopped working. It is not likely that you will resume sperm production. In some cases sperm was produced but production has stopped early. Other people have a genetic disorder and have never produced sperm. This can occur with conditions such as Kleinfelters syndrome where there is an extra X chromosome (XXY) or where there is a microdeletion on the Y chromosome stopping a crucial aspect of sperm production. Sometimes hormones are normal if the sperm making process is arrested at a later stage. It is illegal to use immature sperm in treatment in the UK.
Recently there have been several reports from the USA of retrieving very small amounts of sperm in young men with Kleinfelters, and others with testicular failure, but the chance of success even in their hands is about 25%
If the FSH hormone is low or normal then it is possible that sperm are still being produced in the testis. If the Testosterone level is low then it is possible that although the testes are capable of producing sperm they are not getting the correct hormonal messages from your body. This is correctable.
If the testosterone and FSH hormone are normal you may well have obstructive Azoospermia. There may be a block in the ducts that transport the sperm to the outside world. This may be caused by past infection such as chlamydia or by surgery for some urinary condition.
Unusually when there is no sperm you may prove to have a variant of cystic fibrosis. In this condition the fluid in the testis is unusually sticky and the sperm cannot get out. This can be tested by a blood test. If you do have this it is important that your partner is also tested to see if she is a cystic fibrosis carrier. If she is you should get genetic advice before treatment as there may be some risk of having a child with a more severe variant of the condition. This is a serious condition for the child
If you have either of the last 2 conditions it may be possible to extract small amounts of sperm from the testis and use this. As the amount collected is small you would have to have the treatment called Intra Cytoplasmic Sperm Injection (ICSI). Please see the relevant section in the website.
A few men have no sperm in the ejaculate because they ejaculate into the bladder+. These sperm can be identified and used in treatment. In order to do this the urine has to be made alkaline (it is naturally acid) as an acid environment kills sperm. Urine is collected after ejaculation and centrifuged. The collected sperm may be used for IVF/ICSI or occasionally intra-uterine insemination.
Usually the men affected have either a neurological condition or diabetes.