Apotemnophilia is a disorder characterized by the intense and long-standing desire for amputation of a specific limb. In recent years the word apotemnophilia has come to be seen to carry pejorative overtones, meaning as it does "a love of amputation" and implying that the condition is a sexual paraphilia. In an attempt to move towards a more neutral term for desiring an amputation McGeoch, Brang and Ramachandran proposed that the desire for an amputation be renamed "xenomelia", which derives from the Greek to mean foreign limb. Another term for the condition is body integrity identity disorder (BIID), but this has come to apply to not only those who desire an amputation but also those who want a range of disabilities including deafness, blindness and a spinal cord injury.

Apotemnophilia (xenomelia) has features in common with somatoparaphrenia. Some apotemnophiles seek surgeons to perform an amputation or purposefully injure a limb in order to force emergency medical amputation. A separate definition of apotemnophilia is erotic interest in being or looking like an amputee. This separate definition should not be confused with acrotomophilia, which is the erotic interest in people who "are" amputees.

Apotemnophilia (xenomelia) was first described in a 1977 article by psychologists Gregg Furth and John Money: "Apotemnophilia: two cases of self-demand amputation as paraphilia." Until recently, the primary explanation for Apotemnophilia was psychological/psychiatric, however recent research suggests that here may be a neurological etiology for this disorder.

Apotemnophia / Body Integrity Disorder (BIID) is a is a rare, infrequently studied and highly secretive condition in which there is a mismatch between the mental body image and the physical body. Apotemnomphilia is characterized by an intense desire for amputation of a limb. Currently BIID is not included in the International Statistical Classification of Diseases 11 or the Diagnostic and Statistical Manual of Mental Disorders IV. It is often not known to surgeons, neurologists and psychiatrists. BIID individuals typically avoid healthcare and often act out their desires by pretending they are disabled or perform actual self-amputation.

A 2012 study concluded, based on interviews with 54 individuals, that the main rationale for their desire for body modification (amputation) was to feel complete or to feel satisfied inside. Based on the results of the survey, researchers concluded that psychotherapy was often supportive, but did not help diminishing BIID symptoms. Individuals reported that antidepressants were helpful in reducing depressive symptoms related to BIID, but that antipsychotics were not. Actual amputation of the limb was effective in all 7 cases who had surgical treatment.

Supernumerary body parts are most commonly a congenital disorder involving the growth of an additional part of the body and a deviation from the body plan. Body parts may be easily visible or hidden away, such as internal organs.

Many additional body parts form by the same process as conjoined twins: the zygote begins to split but fails to completely separate. This condition may also be a symptom of repeated occurrences of continuous inbreeding in a genetic line.

Specific types of additional body parts include:

- Accessory breast – one or more additional breasts

- Accessory spleen – one or more additional spleens

- Cervical rib – an additional rib

- Diphallia - Having two penes/penises.

- Hermaphroditism – having both sexes' sex organs

- Hyperdontia – additional teeth

- Pelvic digit – a bony growth in the soft tissue of the pelvic region

- Polycephaly – an extra head

- Polydactyly – additional fingers or toes

- Polymelia — an extra arm or leg.

- Polyorchidism – having three or more testicles

- Supernumerary bones – these additional bones are fairly common, particularly in the feet, and are frequently mistaken for fractures on x-rays.

- Supernumerary kidney – a third kidney

- Supernumerary nipples – an additional nipple

- Supernumerary phantom limbs – where the brain acts as though a limb were there, but it is not.

- Syndactyly – webbing between the fingers or toes

- Uterus didelphys – two vaginal canals and/or uteri