The onset and termination of menstruation is subject, like all other sexual phenomena, to immense variation. It has been known for a girl to start menstruating at three months old (H. Jolly in “Sexual Precocity”, Proc. Royal Soc. Med. 44, 1951), and occasionally the menopause too occurs at a very early age: there are instances of girls reaching the menopause before the age of twenty. The menopause rarely occurs after the age of fifty-five but rare cases do occur. In one instance menstruation was continuing in a woman aged 104.