Amenorrhoea is described as being 'primary' if a woman has never had a period or 'secondary' if a woman has had periods in the past but they have now stopped. Primary amenorrhoea is defined as an abscence of a period by the age of 16 (or 14 in the abscence of secondary sexual characteristics e.g. breasts and pubic hair). Secondary amenorrhoea is defined as an abscence of periods for 6 months.

There are many potential causes of amenorrhoea. The most common are pregnancy and the menopause. There are many other causes which are too numerous to mention but they include developmental abnormalities of the uterus and vagina, polycystic ovarian syndrome, ovarian failure, annorrhexia nervosa, thyroid disease, and a disorder of the pituitary gland called hyperprolactinaemia.