Endometriosis (say "en-doh-mee-tree-OH-sus") occurs when cells that are like the cells that line the inside of your uterus grow outside of your uterus. These cells form growths that often attach to the ovaries or other organs, and they may bleed during your period and cause pain. They may also make it hard for you to get pregnant.
Endometriosis can be treated with medicines or with surgery.