This is a rather atypical case of endometriosis with a large mass infiltrating the uterus (cervix and isthmus) and rectosigmoid colon. There is no evidence of bleeding within the expansion, which is a typical sign of endometrioma. However, there is fibrosis with retraction effect. Glandular appearance is also very rare in endometriosis. Transvaginal biopsy confirmed the diagnosis of endometriosis.