1. Mild or stage / grade I endometriosis appears as small patches or surface lesions scattered around the pelvic cavity.
2. Moderate or stage / grade I or II endometriosis appears as larger widespread disease starting to infiltrate tissue and often found on the ovaries, uterosacral ligaments and Pouch of Douglas. Sometimes there is also significant scarring and adhesions.
3. Severe or stage / grade IV endometriosis affects most of the pelvic organs, often with distortion of the anatomy and adhesions.
These stages of endometriosis are accepted worldwide and described by the American Society of Reproductive Medicine. They provide a useful tool but have limitations as well. For instance the extent of endometriosis is not generally related to the symptoms experienced.