There is no consensus on the classification of endometriosis. The most used system is that of the American Society of Reproductive Medicine (ASRM). This system was designed with a focus on the impact on fertility and not necessarily the impact on patients' quality of life. Endometriosis is classified into four stages depending on the location, extent and depth of endometriosis implants and adhesions.

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• Stage 1, minimal endometriosis (5 points or less), also called superficial peritoneal endometriosis
  The lesions are small and superficial. Scar tissue is minimal or non-existent.
   

• Stage 2, mild endometriosis (between 5 and 15 points), endometriomas
  More injuries and and they tend to be located deeper inside the tissue. There may be some scar tissue, but there is usually no inflammation yet.
   

• Stage 3, moderate endometriosis (between 16 and 40 points), also known as deep infiltrative endometriosis
  Presence of multiple and deep endometriosis implants. There may be endometriomas or chocolate cysts on the ovaries. These cysts are formed when implants surround the ovaries and when they bleed, they leave old brown blood that collects in a capsule that can grow and be very painful when they leak. These bands of scar tissue can fuse the organs together.
   

• Stage 4, severe endometriosis (more than 40 points), or abdominal wall endometriosis  
  Infertility at this stage is very likely due to distortion of the morphology of the abdominal wall. It is characterised by numerous and deep implants. The implants can be in the fallopian tubes and intestines. Endometriosis adhesions can be thick and deep and cause severe pain. There may be numerous and/or large cysts on the ovaries, and between the uterus and rectum.
   

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