Gender identity disorder is a persistent feelings that your body is a different gender than your mind. It is a sense of inappropriateness of one's anatomic sex.

Boys with gender identity disorder see themselves as girls and vice versa. This is distinct from homosexuality -- people with gender identity disorder may be attracted to the same or the opposite sex, but they feel that their own biological sex is "wrong" and doesn't represent their true gender identity.

People with gender identity disorder act and present themselves as members of the opposite sex. The disorder affects self-concept, choice of sexual partners, and the display of femininity or masculinity through mannerisms, behavior, and dress.

The feeling of being in the body of the "wrong" gender must persist for at least 2 years for this diagnosis to be made. The cause is unknown, but hormonal influences in the womb, genetics, and environmental factors (such as parenting) are suspected to be involved. The disorder may occur in children or adults, and is rare.