Endometriosis is a fascinating disease--it is common and occurs with increasing frequency. The aetiology remains obscure, but Sampson's theory of retrograde menstruation and implantation is still the most popular and widely accepted. Certain factors play an important role in, predispose to, or stimulate the development of endometriosis. Although the disease can be cured by the menopause, or hysterectomy and bilateral salpingo-oöphorectomy, permanent cure by conservative means is difficult. Better and more effective ways of treatment will solve only part of the problem, and the real solution is prevention of the disease.