Boys will be boys, or so the saying goes. But what happens when boys want to be girls? Or girls want to be boys? Some people feel that their body does not match who they are on the inside. Some choose to present themselves as the gender they identify with through clothing and cosmetics. Others change their physical appearance through hormones and surgery. This is called gender identity disorder, or GID, also known as gender identity confusion, gender dysphoria, transgenderism and transsexualism.

Mental health professionals believe there are three components that make up our gender identity: our sexual orientation, behavior and mannerism preferences, and core gender identity (that gut feeling we have about the gender we identify with). In most of us, these three components and our anatomy align as male or female. For some, however, these components don't all match up.

The cause of gender identity disorder is still being debated. Theories suggest it is caused by genetic abnormalities, endocrine problems like a testosterone or estrogen imbalance in the womb, social factors like parenting or some combination of issues [source: Merck].

Gender identity disorder may manifest in children, adolescents or adults, and appears more frequently in males than in females [source: WebMD]. While there are no recent statistics to show us how prevalent gender identity disorder is, we do know that an estimated 1 in 30,000 adult males and 1 in 100,000 adult females seek gender reassignment surgery, a treatment chosen by some people with GID [source: Merck].

At what age do parents begin to see symptoms of GID in children? Keep reading to learn about treatment and diagnosis.