People who are transgender -- that is, those who self-identity doesn't match their biological sex -- were long classified as having a psychological disorder. Specifically, the American Psychiatric Association called the condition "gender identity disorder" and added the term to its Diagnostic and Statistical Manual of Mental Disorders, or DSM, in 1980 [source: Glicksman]. Although assigning transgender people this label ensured they had access to medical care, the term "disorder" carried a certain stigma.
In the fifth edition of the DSM, published in 2013, the term "gender identity disorder" was replaced with "gender dysphoria," a less stigmatizing term [source: Lowder]. This is an acknowledgement that being transgender is simply something that can happen to human beings. It's not a disorder in and of itself. You can be transgender and not seek or need treatment of any sort. However, if you have such intense distress being in the "wrong" body that you want to transition to the male or female form, that is considered having gender dysphoria. Physicians with transgender patients who have gender dysphoria are generally required to first be assessed by a mental health professional before undergoing any kind of medical intervention.