Gender dysphoria is a condition in which a person feels that they are trapped within a body of the wrong sex. It can also be known as gender identity disorder, gender incongruence or transgenderism. People who have long-lasting, extreme cases of this condition are known as transsexuals.

A person with gender dysphoria experiences anxiety, uncertainty or persistently uncomfortable feelings about the gender they were born with. They believe their gender identity is different from their anatomical sex. For example, a man with gender dysphoria feels that he is a female, but was born into a male body.

Gender dysphoria is rare, but increasing numbers of people with the condition are becoming known due to growing public awareness. However, many people with gender dysphoria still face prejudice and misunderstanding of their condition.

It is estimated that one in 4,000 people in the UK is receiving medical help for gender dysphoria, which suggests that there are many more people with the condition who have yet to seek help. On average, men are diagnosed with gender dysphoria five times more often than women.

The symptoms of gender dysphoria usually appear at a very young age. Children may refuse to wear typical boys' or girls' clothes, or dislike taking part in typical boys' or girls' games and activities. In most cases, this kind of behaviour is just a normal part of growing up, but in cases of gender dysphoria, it persists into later childhood, adolescence and adulthood.

The exact cause of gender dysphoria is unknown. It is currently classed as a psychiatric condition (relating to the mind), but many recent studies have suggested that it is more to do with biological development (relating to the body). There is ongoing research into what causes it.

Treatment for gender dysphoria helps people become content with their gender identity. For some people, this means  dressing and living as their preferred gender. For others, it may involve taking hormones that change their physical appearance. For most transsexuals, it means having surgery to permanently alter their anatomical gender.

Since the Gender Recognition Act was passed in 2004, people with gender dysphoria and transsexuals can marry in their preferred gender. They can obtain legal documentation stating their preferred gender, including a new birth certificate and passport.