The World Health Organization removed “transsexualism” from the International Classification of Diseases, a diagnostic manual of illnesses used by most countries around the world.

The change was announced earlier this week as part of the newest version of the manual, the ICD-11. The removal of “transsexualism” means transgender people will no longer be classified as having a mental illness by the WHO, an international public health agency run by the United Nations. The diagnosis of “transsexualism” was renamed “gender incongruence” and moved from the “Mental and Behavioral Disorders” chapter to the “Conditions Related to Sexual Health” chapter.

“This is a historic move,” Sam Winter, a public health professor at Australia's Curtin University, told NBC News via email. “An end to a classification that was a historical artifact, had little basis in science, and had massive consequences for the lives of trans people.”

Winter is a member of the WHO Working Group on Sexual Disorders and Sexual Health, which advised the organization on ICD-11. He said the new language — "gender incongruence" — focuses on “how the person identifies” and enables “the diagnoses to be used with non-binary people as well as those who identify as boys/men and girls/women.”

The updated ICD does not remove diagnoses for trans people entirely. Winter said to do so would be counterproductive.

"Quite a few trans people seek substantial ongoing healthcare — it can be life changing, or even life saving. So we need a diagnosis.”

ICD-11 also removes what “residual” diagnoses remained for same-sex attraction that were used to justify “reparative therapies” for gays, lesbians and bisexuals. Winter called it a "historic step."

“Finally, with ICD-11, we have an end to the pathologization of same sex attraction and behavior,” he said.

The WHO said it moved the newly renamed “gender incongruence” to its list of “sexual health conditions" because "while evidence is now clear that it is not a mental disorder, and indeed classifying it in this can cause enormous stigma for people who are transgender, there remain significant health care needs that can best be met if the condition is coded under the ICD.”

Kyle Knight, a LGBTQ researcher with Human Rights Watch, said more than 70 percent of global psychiatric practitioners use the ICD to code their patients, and that the past categorization of "transsexualism" as a mental disorder was a “contributing factor behind a lot of the human rights violations that trans people face.”

The new ICD, Knight said, is a “high-level social sanction for the very existence of this population.”

A diagnostic code in a country that follows the ICD makes it easier to provide health care, but before now, transgender people had to receive a diagnosis of a mental illness in order to access appropriate health care like hormone replacement therapy.

The ICD is used in most countries except for the United States and Canada, where psychiatrists follow the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM).

"Homosexuality" was removed from the DSM’s list of mental disorders in 1974, but its successor, "sexual orientation disturbance," wasn't dropped until 1987. DSM-5, the newest iteration published in 2017, removed “gender identity disorder” from its list of mental disorders and replaced it with “gender dysphoria,” which is applicable only when the person is significantly distressed by the mismatch between their assigned sex and gender identity.

Knight said some countries already have progressive gender identity laws on the books, like Nepal and India, two countries that have a long tradition of “third gender” people in their societies. The new ICD may not impact their rights, but it could have an impact on the ease with which they access relevant medical care. In other countries with weaker protections for gender minorities, Knight said the new ICD may end up having a political impact.

Winter said the next big question is what will the American Psychiatric Association do, because the DSM is still a compendium of mental disorders and thus categorizes some people as disordered if they meet the threshold for “gender dysphoria," or GD.

“Will APA follow ICD’s lead, in this case by removing the GD diagnoses from the manual?” Winter asked.

While Winter is satisfied with many of the changes in ICD-11, he expressed disappointment that “gender incongruence of childhood" (GIC) — essentially pre-adolescent transgender identity — is still listed in the manual.

“We look forward to the day when GIC comes out of ICD,” he said. “It has no place anywhere in the manual; not even in 'Conditions Related to Sexual Health.'”

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