Is being transgender a mental illness/disorder?

No. Classifying gender identity as a medical condition has been problematic. Those whose gender is simply different to the one they were assigned at birth understandably do not wish to be classified as having a disease, or a disorder, or an illness. Previous Classifications of Diseases (ICD) have classified gender-identity related health as Gender Identity Disorder in a category of mental health. However, it is no longer considered a disorder. ICD-11 now classifies it as ‘gender incongruence of adolescence and adulthood’ and ‘gender incongruence of childhood’ in a category of matters related to sexual health.