Endometriosis is a medical condition in which tissue similar to the lining of the uterus (endometrium) grows outside of the uterus. This tissue can be found on the ovaries, fallopian tubes, outer surface of the uterus, and other organs in the pelvis. Endometriosis can cause pain, heavy periods, infertility, and other symptoms. It is a chronic condition that affects women of reproductive age. Treatment options include medication, surgery, and lifestyle changes.