A Chinese man who went to the doctors with a swollen stomach was told that he is actually a woman.
The 66-year-old, who even has a beard, had lived his entire life as a man but was told by doctors in Hong Kong that his enlarged abdomen was caused by an ovarian cyst.
Tests revealed the patient suffered two rare genetic disorders that had gone undiagnosed.
They showed the patient had Turner Syndrome, a genetic condition that affects about one in 2,000 baby girls, and congenital adrenal hyperplasia, which increases male hormones.
The Hong Kong Medical Journal, which published the information yesterday, said only six cases of people with both disorders had ever been reported in medical literature.
Turner Syndrome usually results from a problem with the chromosomes and can leave women infertile and shorter than normal.
Women with the syndrome are missing one or part of their second X chromosome.
Congenital adrenal hyperplasia affects one in around 15,000 births and causes male characteristics to appear early or inappropriately.
The patient had grown up an orphan and stopped growing after puberty at the age of 10 and was just 4.5ft tall.
The patient also had no testes and a 'micro-penis', according to the report.
Girls with the disorder have normal female reproductive organs but can suffer with fertility problems.
Seven doctors, writing in the medical journal, said the Vietnam-born patient would continue to live as a man and may be treated with testosterone replacement.
They said: 'Were it not due to the huge ovarian cyst, his intriguing medical condition might never have been exposed'.