Menopause, a normal biological phenomenon affecting all women, is the period of life after the last menstrual period characterized by permanent cessation of ovarian function. The transitional period before and after the definitive cessation of ovarian function is called climacteric, a name that tends to be replaced by the term perimenopausal period. In European countries and the USA the average age of menopause is between 49–51 years. 

A significantly lower age has been reported in countries with a lower standard of living. However, the factors that determine the age of menopause are not known, although a hereditary predisposition is mentioned, nor is there a correlation with the age of menarche, cycle type, number of pregnancies or sex life. Also, menopause occurs earlier in smokers.

The onset of menopause between 40–50 years is characterized as early. Before the age of 40 is characterized as premature menopause, or better as premature ovarian failure, with a frequency of ~1% in women of reproductive age and in most cases its etiology is unknown. Primary ovarian insufficiency is a disorder in women younger than 40 years of age that is characterized by a decline in ovarian function, loss of oocytes and folliculogenesis, and elevated gonadotropin levels; it leads to compromised fertility and marked reduction of ovarian hormone production. This condition arises from a premature decrease in the number of ovarian follicles, acceleration of follicle destruction, or poor follicular response to gonadotropins. The reduction in systemic estrogen before the age of natural menopause is associated with the development of osteoporosis, cardiovascular disease, and possibly accelerated neurodegenerative aging.

30–50% of women with premature ovarian failure have autoantibodies against steroid-producing cells, with lymphocytic infiltration of the ovaries on biopsy and the presence of another autoimmune endocrinopathy (eg, myasthenia gravis, Hashimoto's thyroiditis). Other causes are iatrogenic, such as surgical removal, destruction due to chemotherapy (cyclophosphamide, busulfan) or ovarian radiation (~800 rads at age >30 years).

GRADUATE COURSES IN ENDOCRINOLOGY AND DIABETES- DEPARTMENT OF ENDOCRINOLOGY DIABETES AND METABOLISM OF EVANGELISMOS GENERAL HOSPITAL OF ATHENS- 2004