In an extremely unusual case, a Kolkata doctor is treating a teenage boy who has been showing symptoms of menstruation.

The 15-year-old 'effeminate' boy's bleeding has been occurring in the second week of every month and lasts three days. During the period he experiences stomach aches, cramps, nausea and mood swings.

"We examined the boy. Though he has male organs, his behaviour and traits are like a woman," said physician Sudip Mondal.

"If tests of blood samples prove the presence of ovum, this would be a very rare medical case," he added.

Tarak, the boy who was identified by only one name, works as a domestic help in Kalna town, some 200 km north of Kolkata.

He began 'menstruating' more than a year ago, but hid the fact from his employers and his impoverished family for the fear of losing his job.

Doctors, who say this is a very rare case but not unprecedented, are now planning chromosomal and hormonal tests on the boy.

"The presence of female functional endometrial in a male prostrate gland can cause this type of anomaly," said Pradip Mitra of the West Bengal Gynaecological Society.

"The boy needs immediate medical attention or else this could cause fatal complications," Mitra warned.