Technically, menopause is the ceasing of menses, while the process in which this occurs is the climacteric and takes place gradually over a year, but may take as little as six months or more than five years. Popular use however replaces climacteric with menopause.
The average onset of menopause is 50.5 years, but some women enter menopause at a younger age, especially if they have suffered from cancer or another serious illness and undergone chemotherapy. Premature menopause (or Premature Ovarian Failure) is defined as menopause occurring before the age of 40, and occurs in 1% of women. Other causes of premature menopause include autoimmune disorders like thyroid disease or diabetes mellitus. Premature menopause is diagnosed by measuring the levels of follicle stimulating hormone (FSH) and luteinizing hormone (LH); the levels of these hormones will be higher if menopause has occurred.
Some women see menopause as being a normal stage of their life-cycle and one which will eventually pass by itself without medical intervention. Some doctors would disagree with that view, and medical 'treatments' for menopausal symptoms have been developed, eg. Hormone Replacement Therapy (HRT). This is seen as sexist and mostly harmful by some.
Post-menopausal women are at increased risk of osteoporosis, mostly among European women.