An orchiectomy (spelled orchidectomy in British English), is the medical term for the surgical procedure to remove one or more of the testicles. A bilateral orchiectomy is the removal of both testicles and is commonly referred to as castration.

An orchiectomy doesn't remove the penis, which would be a penectomy. It is also different from a vasectomy, which leaves the testicles and their function intact while still causing sterilization. While sex reassignment surgery (SRS) for male to female transsexuals also removes the testicles and penis, it is different because it also creates a functional vagina in the process.

The effects of an orchiectomy are caused by the reduction of testosterone. They can vary based on the age of the person and on the number of testicles removed.

If castration is done prior to puberty then the person won't develop male secondary sex characteristics without testosterone replacement therapy.

These Include:

• Deep voice
• Male body hair
• Balding
• Facial hair
• Muscular frame
• Reduced or complete lack of sex drive
• Possible slight breast growth

If Castration is Done After Puberty:

• Loss of body hair
• Loss of muscle mass
• Increased body fat
• Possible reduced sex drive
• Possible slight breast growth 
• Prevent or stop baldness

In most cases of castration after puberty facial hair growth is slowed but not stopped, libido is reduced but still exists and the voice remains deep.

If only one testicle is removed, the other testicle increases testosterone production and there won't be too much of a change.

Male to female (MTF) transsexuals, as well as some other transgendered people, sometimes undergo orchiectomy. An orchiectomy can be done before or instead of sex reassignment surgery (SRS). This is an option for those that either can't afford, aren't in good enough health or do not want to have SRS.

It is often recommended to get a bilateral orchiectomy when anti-androgens such as spironolactone or cyproterone acetate cause unwanted and dangerous side effects. Kidney, liver, and thyroid damage are common after long term use. There is also an increased risk of blood clots, hyperkalemia and some people are allergic to the medications.

1. Ability to stop taking anti-androgens and reduce estrogen
2. Increased health from reduction of medications
3. Saves money on medications
4. Might be able to legally change sex with an orchiectomy
5. Easier to "tuck" and hide genitals
6. Taken more seriously by society
7. Increased body image
8. Improved and faster feminization
9. Can no longer have testicular pain
10. Never detransition even if you can't take medications

There are also some possible downsides to getting an orchiectomy if you are planning on later sex reassignment surgery (SRS). The scrotal skin could possibly shrink resulting in less for later, and the money could have been saved for SRS. However, if you aren't close to affording SRS then you can save on medication costs. If an orchiectomy is done improperly then there is the chance of scar tissue.

Some surgeons might charge more for sex reassignment surgery if you have had an orchiectomy. Dr. Suporn is well known for refusing patients or charging a fee if you have been castrated.

The most common reason for an orchiectomy is as a treatment for testicular cancer. If only one testicle is found to be cancerous then only that one is removed. Even if both testicles are removed, male sexual function can be restored and maintained through the use of testosterone injections or patches. However without testicles there is no production of sperm and so the person will be infertile.

Some men seek this procedure in order to remove what they consider uncomfortable, uncontrollable or dysfunctional sexual urges. Others may seek it in order to fulfill a fetish or fantasy. The most common reason for control of sexuality is as part of rehabilitation for sex offenders.

There are also eunuchs, which get castrated for religious or alternative gender identities.