Gender, sex, sexuality and intimacy – these words seem to mean the same thing, but actually define very different aspects of our gender and sexuality. With the recent news that the World Health Organization has removed “gender incongruence” from the chapter on Mental and Behavioural Disorders in the 11th revision of the International Classification of Diseases (ICD-11), and reclassified it as a sexual health condition, we speak to rehabilitation physician Dr Intan Sabrina Mohamad on the biological perspectives of gender, sex and sexuality.