Menopause represents the end of menstruation, usually diagnosed when a woman has not had a menstrual period for 12 consecutive months, and there is no other obvious biologic or physiologic cause.

In the Western world, the majority of women experience a natural menopause between the ages of 45 and 55 --on average at about age 51 --but it can occur as early as in a woman's 30s and as late as in her 60s. Menopause is not a disease, but a natural event --the end of fertility --resulting from the ovaries slowing down production of two sex hormones: estrogen and progesterone. When the ovaries are removed surgically ("surgical menopause") or when the ovaries are damaged through drugs or x-rays, "induced menopause" results. Menopause is considered to be "premature" when it occurs either naturally or is induced before age 40.

Although menopause has been defined as a point time, in truth this is a process which unfolds over many years. These years bring a variety of changes associated with decreasing estrogen levels. These changes or "symptoms" most often start in a woman's 40s and sometimes in her 30s. Many women are surprised by two things: the age at which menopause-related symptoms can begin, and the range of symptoms. Other terms often used to discuss menopause include "pre-menopause" (all the reproductive years leading to menopause), "peri-menopause" includes the time immediately prior to the menopause (when the endocrinological, biological, and clinical features of approaching menopause commence) as well as the first years immediately after menopause, and "post-menopause" (all the time beyond menopause).

Before menstruation stops completely, most women experience noticeable changes in their periods. Some periods become shorter in length; others become longer. The flow may be lighter or heavier --and some women have extensive bleeding with clots. The time between periods often changes, with irregularity being very common.

Many women ask when they will go through menopause. Family history might provide clues, since the time of menopause is determined genetically; however, recalled dates of a mother's or grandmother's menopause may not be accurate. Contrary to previous opinion, there is no correlation between the time of a woman's first period and her age at menopause. In addition, in most studies, other factors that have no influence on age at menopause include race, height, the number of children a woman has had, and whether she took oral contraceptives. There is some evidence that a small percentage of women who have had their uterus (but not ovaries) removed --called a "hysterectomy" --experience menopause several years earlier than women of the same age without hysterectomy. One factor that definitely influences the age of menopause is cigarette smoking. Smokers, and even former smokers, can experience menopause up to three years earlier than nonsmokers --providing another reason not to smoke. Although the time of the initial menstrual period ("menarche") is typically experienced at an earlier age than years ago --probably because of improvements in health, education, nutrition, and living conditions --the average age at menopause (about 51 in the Western world) has not changed much since ancient times.

Women who have had hysterectomies and who have not had their ovaries removed will ask when they have gone through menopause. Following "hysterectomy" (the surgical removal of the uterus or womb, but not the ovaries), there will be no more menstrual periods. Therefore, a woman will not have the best marker for identifying menopause: stopping of menstrual periods for 12 consecutive months. However, with the ovaries still intact, estrogen will continue to be produced so that signs of approaching menopause that may appear include the same ones that could appear with a uterus: hot flashes and night sweats. These changes may continue to be experienced or even worsen when the ovaries shut down their production of estrogen at menopause.