The human immunodeficiency virus (HIV) causes AIDS (acquired immunodeficiency syndrome). HIV, discovered in 1983, two years after AIDS, destroys CD4+T cells, progressively damaging the body's immune system until defenses are so lowered that AIDS can develop. 75% to 83% of the CD4+T cells have been eliminated at that point. HIV is thought to have entered the United States in the late 1970s, several years before its existence was realized. Between 1981 and 2002, 886,483 people were diagnosed with AIDS in the United States. 501,640 deaths from AIDS were reported during the same period. The high mortality rate for AIDS has been moderated by modern drug therapies, allowing patients with AIDS to live longer.

HIV is transmitted primarily by sexual contact, sharing needles or syringes, and infected blood. HIV can be present in saliva or tears; it is not found in sweat--none of these three liquids has been shown to transmit the virus.

As of September 2003 the US Centers for Disease Control (CDC) had no evidence that a client had ever infected a therapist. Nonetheless, the CDC issued guidelines in 1985 to discourage contact between skin or mucous membranes and infected blood. Gloves should be worn if contact with infected blood is possible. Cuts, sores or breaks on either the therapist or client should be covered with bandages. Hands or surfaces which come into contact with infected blood should be washed and disinfected.

Massage is used to reduce the pain and stress of the disease.

The law may prohibit a therapist's refusal to treat a patient with AIDS. Standard II (a) of the Standards of Practice require the therapist to "obey all applicable local, state and federal laws." If the therapist is in a jurisdiction with a law requiring treatment of AIDS patients, then the therapist has an ethical duty to do so.

In 1998 the United States Supreme Court held that a dentist violated the Americans With Disabilities Act (ADA) when he refused to treat a person who was HIV positive. This may suggest an ethical obligation under federal law for a therapist to treat. However, a Nebraska employer is using the same ADA to defend against firing an HIV-positive employee, claiming the employee posed a direct threat to other employees and customers.

It is reported that 16% of Canadian dentists have refused to treat patients with AIDS.

There is special training available for those therapists who wish to work on AIDS patients.