First published in 1968, DSM-II (the American classiifcation of mental disorders) listed homosexuality as a mental disorder. In this, the DSM followed in a long tradition in medicine and psychiatry, which in the 19th century appropriated homosexuality from the Church and, in an élan of enlightenment, transformed it from sin to mental disorder.

In 1973, the American Psychiatric Association (APA) asked all members attending its convention to vote on whether they believed homosexuality to be a mental disorder. 5,854 psychiatrists voted to remove homosexuality from the DSM, and 3,810 to retain it.

The APA then compromised, removing homosexuality from the DSM but replacing it, in effect, with "sexual orientation disturbance" for people "in conflict with" their sexual orientation. Not until 1987 did homosexuality completely fall out of the DSM.

Meanwhile, the World Health Organization (WHO) only removed homosexuality from its ICD classification with the publication of ICD-10 in 1992, although ICD-10 still carries the construct of "ego-dystonic sexual orientation". In this condition, the person is not in doubt about his or her sexual preference, but "wishes it were different because of associated psychological and behavioural disorders".

The evolution of the status of homosexuality in the classifications of mental disorders highlights that concepts of mental disorder can be rapidly evolving social constructs that change as society changes. Today, the standard of psychotherapy in the U.S. and Europe is gay affirmative psychotherapy, which encourages gay people to accept their sexual orientation.