Hospital doctors who examined a 66-year-old Chinese man to investigate his complaints of a swollen abdomen made a startling discovery in the consultation room - he was a she and did not know it.
Medics were stunned when they realised that the unnamed patient's swollen stomach was the result of an ovarian cyst, the Hong Kong Medical Journal reported.
The unusual case was reported by doctors at Hong Kong's Kwong Wah Hospital and Queen Elizabeth Hospital, where the patient received medical treatment.
Tests revealed that the patient was suffering from congenital adrenal hyperplasia and Turner syndrome, two rare genetic disorders.
Turner syndrome is a condition that results from a problem with the chromosomes and only affects women. Symptoms of the condition include infertility and stunted growth.
People with the syndrome tend to have only one X chromosome, instead of the normal pair, or are missing part of their second X chromosome.
Congenital adrenal hyperplasia increases male hormones and makes the patient, who doctors noted had a beard and a "micropenis", appear more masculine.
The patient disclosed a long history of urinary leakage and stunted growth after the age of 10 years.
"Were it not due to the huge ovarian cyst, his intriguing medical condition might never have been exposed," a study in the Kong Medical Journal said.