Endometriosis is a painful disorder in which the endometrium, the tissue that lines the uterus, grows outside of it.  This generally occurs in the linings of the abdomen and pelvic cavity.  Its main symptom is pain during menstruation, also known as dysmenorrhea.  Other symptoms include chronic pelvic pain and infertility.  Worldwide, it is estimated that 1 in every 10 women of reproductive age is affected by endometriosis including approximately 9 million women in the United States, and 50 thousand in Puerto Rico.