Menopause is a natural biological process. It is a time in a woman's life when her menstrual cycle has ended. It is not an illness. It does not happen suddenly, but gradually. There are three stages: Perimenopausal/transition, menopause, and postmenopausal. The pre-menopausal stage begins about 4 years before the last period. Menopause can happen in the early 40's or late 50's.