How are the stages of endometriosis determined?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Endometriosis is classified into four stages based on the location, size, depth, and amount of endometrial-like tissue growing outside the uterus. Doctors typically use imaging tests such as ultrasound or MRI, and sometimes laparoscopic surgery, to accurately determine the stage.

Stage 1 (Minimal): Few small, shallow growths
Stage 2 (Mild): More growths, slightly deeper
Stage 3 (Moderate): Many deep growths, possibly small cysts
Stage 4 (Severe): Many deep growths, large cysts, and dense adhesions

Importantly, the stage does not always reflect symptom severity — some people with Stage 1 experience intense pain, while others with Stage 4 have few symptoms.

Because endometriosis symptoms often overlap with other conditions, identifying what's really going on can be difficult without guidance. Taking a free, instant, online symptom check can help you clarify your symptoms, understand possible causes, and confidently plan your next steps — all in just a few minutes and from the privacy of your home.

Reviewed for medical accuracy: 07/15/2026

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Explanation

Endometriosis is a condition where tissue similar to the lining inside the uterus grows outside of it. The stages of endometriosis are determined by how much tissue there is, where it is located, and how deeply it grows into organs.

Stage 1 (Minimal): There are only a few small growths or implants. They are usually shallow and not very deep.
Stage 2 (Mild): There are more implants than in stage 1, but they are still shallow.
Stage 3 (Moderate): There are many deep implants. There may also be small cysts on one or both ovaries and thin bands of scar tissue called adhesions.
Stage 4 (Severe): This is the most advanced stage. There are many deep implants, large cysts on one or both ovaries, and many dense adhesions.

If you're experiencing symptoms that concern you, you can use Ubie's free AI symptom checker to better understand what might be happening with your body. Doctors use imaging tests like MRI, as mentioned in the ENDO_STAGE study, to help see where the tissue is and how much there is. Sometimes, doctors need to do surgery to look inside the body to determine the stage. This helps them decide the best treatment.

(References)

Pašalić E, Tambuwala MM, & Hromić-Jahjefendić A. (2023). Classification, pathophysiology, and treatment options. Pathology, research and practice, 37844487.
Bazot M, Daraï E, Benagiano GP, Reinhold C, Favier A, Roman H, et al. (2022). ENDO_STAGE Magnetic Resonance Imaging. Journal of clinical medicine, 35566569.
Weitzman GA, & Buttram VC Jr. (1989). Classification of endometriosis. Obstetrics and gynecology clinics of North America, 2664623.

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