The scientific term for this condition is gender identity disorder. "Trapped" will be broadcast on Wednesday, Feb. 25, at 10 p.m. ET/PT.
Contributing Correspondent Maureen Maher speaks to Kayla, an 11-year-old girl who is convinced she should have been born a boy. Last year, Kayla made some drastic changes: a new haircut, a new school and even a new name.
Now Kaden, as her friends and family call her, wants to start taking hormones to stop her body from going through the female stages of puberty. And Kayla's mother, Angelina, has an agonizing decision to make about whether to allow her daughter to continue her journey to becoming a boy.
"I've lost my little girl," says Angelina. "But if I hold Kaden back from who he wants to be, then I'm going to hurt him as a person."
Angelina takes Kaden to several therapists and physicians who will help them make this monumental decision.
Also in the hour, Jenny Boylan, a respected college professor and author from Maine who was once known as James, speaks to Correspondent Susan Spencer about becoming a woman at age 40, and how it has affected her children, her wife, her colleagues and friends.
Boylan tells Spencer, "If people see someone like me, they think, well, that person must be gay. Or they think, well, that person's cross-dressing. ... And none of those things are true."
Dr. Kathleen Farrell, a therapist who has been treating transsexuals for 20 years, says: "A transsexual is a person whose brain sex is different from their body gender. It is something that a person is born with and there is no other choice for them. ... There is no way to escape this. It is on that person's mind all the time."
Experts aren't sure what causes transgenderism, but one study found telltale structural differences in the brains of transsexuals, particularly in the hypothalamus, which is associated with gender and sex. Male transsexuals have brains that look more liked women's than like other men's.
Correspondent Troy Roberts interviews Jennifer Edwards, a 47-year-old from Oldsmar, Fla., who elected to undergo sexual reassignment surgery.
48 Hours Investigates follows Jennifer through the yearlong process, which proves to be extremely challenging both physically and psychologically. There are now dozens of doctors in the U.S. who perform this kind of surgery, usually on men who want to become women.