The prevalence of endometriosis is not accurately known although estimates vary greatly, it is believed to affect around 10% of women of reproductive age. It is also associated with infertility in up to 40% of women dependent upon the age of diagnosis. A more recent in-depth study in women over the age of 16 years, however, showed a prevalence closer to 1.44%. The peak incidence is 40 years of age and endometriosis symptoms usually resolve with the onset of the menopause. There are racial and ethnic variations with the highest prevalence amongst Asian women, followed by Caucasian with African women the least frequently affected.
In a large survey of over 70,000 adolescent women, dysmenorrhoea (painful periods) was a common cause of reported school absence. In the United States chronic pelvic pain affects approximately 1:7 women with very high associated annual health costs. A Norwegian study demonstrated that 2% of women had been treated for this condition by the age of forty. Endometriosis associated pain may be found in up to 60% of women with dysmenorrhoea and 40-50% of women with pelvic pain and dyspareunia (pain during sexual intercourse). Despite the identification of endometriosis symptoms there is often delay in establishing a diagnosis of endometriosis and hence a delay in ensuring effective treatment. This delay is up to 7 years and a consistent feature of most female populations.