"The American Psychiatric Association, publisher of the DSM-5, states that 'gender nonconformity is not in itself a mental disorder. The critical element of gender dysphoria is the presence of clinically significant distress associated with the condition.'"

Link

As for the ICD,

"Sexual orientation by itself is not to be regarded as a disorder."

However, it seems that its definition of gender dysphoria, in the ICD called "gender maturation disorder," is similar to the DSM's in that it's only a disorder when it causes anxiety and/or depression.

"Sexual maturation disorder

The patient suffers from uncertainty about his or her gender identity or sexual orientation, which causes anxiety or depression. Most commonly this occurs in adolescents who are not certain whether they are homosexual, heterosexual or bisexual in orientation, or in individuals who, after a period of apparently stable sexual orientation (often within a longstanding relationship), find that their sexual orientation is changing."

Link