Endometriosis is generally classified into four stages based on the extent and severity of the condition, according to the revised American Society for Reproductive Medicine (rASRM) staging system:

1. Minimal (Stage I): In this stage, there are isolated implants and no significant adhesions.

2. Mild (Stage II): Implants are more numerous, and there may be some scarring in the pelvis.

3. Moderate (Stage III): Implants are more extensive, and there are more pronounced adhesions involving the ovaries and fallopian tubes.

4. Severe (Stage IV): This is the most advanced stage, characterized by extensive implants, severe scarring, and adhesions often involving multiple pelvic organs, such as the ovaries, fallopian tubes, bladder, and bowel.

Another classification system commonly used for endometriosis is the Enzian classification, which provides a more detailed assessment of the disease based on its morphological characteristics. The Enzian classification categorizes endometriosis lesions into different types:

1. Superficial peritoneal endometriosis (SUP): Involves lesions on the peritoneum.

2. Ovarian endometriomas (OMA): Endometriosis affecting the ovaries, forming cysts known as endometriomas.

3. Deep infiltrating endometriosis (DIE): Characterized by lesions that penetrate deeply into the surrounding tissues, such as the rectovaginal septum, bladder, bowel, and other pelvic structures.

4. Adenomyosis externa (ADENEX): Endometrial tissue located within the outer myometrium layer of the uterus.