The large brown envelope that made sense of Melissa's troubled past arrived in the post shortly after her 18^th birthday. Melissa took the package to the privacy of her bedroom before breaking the seal on information she hoped would explain the feelings of shame and secrecy that had dominated her childhood and the reasons for the repeated gynecological surgery she had endured. She was shocked and angered by what she read.

As Melissa was growing up, she had been told that she suffered from a rare metabolic disorder that caused her body to lose excessive amounts of salt and led to her being placed on medication she would need for the rest of her life.

She knew she had been a small, sickly baby who had not been expected to survive. She knew the condition she was born with was called congenital adrenal hyperplasia (CAH). What she was not told, but discovered from the information sent to her that day, was that CAH is an "intersex" condition. She had been born of mixed gender, with ambiguous-looking genitalia, neither wholly female nor male.

"I was told as I was growing up that something was 'not quite right down there'. But I was also told not to ask too many questions. I thought it must be something horrible," Melissa, now 33, recalls. "My mother just told me that I should always use a cubicle to change at school and that nobody but a doctor was ever allowed to touch me."

When Melissa confronted her mother, and asked her why she had never been told the truth, "She said she thought the truth would upset me," says Melissa. "She told me for the first time that doctors had thought I was a boy when I was born, and that she and my father had named me Nicholas." But when doctors pumped dye through her genital tract when she was three weeks old, they discovered Melissa had a womb and ovaries. "My parents were told I was a girl after all, but that I would need surgery to 'normalise' things. I was devastated. Not that I was intersex, but that I had been lied to."

After requesting that her medical records be released to her, Melissa discovered that the operations she had undergone as a baby, and later at the ages of 4, 12 and 14, consisted of a complete removal of the clitoris — hers was considered too large. She also underwent extensive reconstruction of her vagina. "The outcome," she says, "was a mess."

Anna was also never told the truth about her condition, or the real reason she underwent surgery at the age of 20. After seeking advice from her doctor about her failure to menstruate, Anna was sent to a London hospital for examination, where she was told she had lumps in her abdomen that needed to be removed. After surgery, she was prescribed a high dosage of the female hormone oestrogen and discharged with little follow-up.

"I felt confused, like something was very wrong. But I didn't understand what was happening," says Anna, now 44. "When I looked through some medical notes that were left by my bed in hospital, I saw someone had written, 'She is not aware of her condition.' When I asked my mother what that meant, she told me never to ask the doctors about it."

In the years that followed, Anna tried to find out more about what had happened to her in hospital. Her mother gave her "a few snippets of information to go on," she says, almost casually, such as the fact that she was born with XY chromosomes, which meant that genetically she had been born male, not female. It was then, she says, that her childhood began to make sense. Anna remembers quite clearly at school feeling she did not belong with the other girls. "I looked like a girl. But I knew I was a boy.

"I always played with the boys. As a teenager I fell in love with girls. But I didn't become sexually active."

What Anna slowly discovered in medical journals was that she had a rare genetic disorder called androgen insensitivity syndrome (AIS), also classed as an intersex condition. This meant that although externally she looked like a girl, she had no womb or ovaries, her vagina was undeveloped, and her body produced high levels of testosterone.

The lumps that doctors removed when she was 20 were undescended testes. "Because they kept what they were doing secret, I had no way of knowing what a huge impact removing this source of testosterone would have on my psyche, no way of objecting to it," says Anna.