Study Objective Presentation of unique case of postmenopausal patient with previous total hysterectomy, salpingo-oophorectomy and excision of endometriosis who developed cancer originating from endometriosis. Design Case report Setting Endometriosis Referral center Patients or Participants This video presents a 78-year-old G1P1 female with a history of endometriosis who presented with post-coital vaginal bleeding. She had a history of a total abdominal hysterectomy at the age of 46 due to pelvic pain, and later underwent bilateral salpingo-oophorectomy and excision of endometriosis at the age of 56 due to continued pain. She was on hormonal supplementation with transdermal estrogen. Preoperative examination and imaging revealed a 5 cm friable mass at the vaginal cuff and a smaller pelvic mass in the left pelvic sidewall. Interventions The patient underwent multi puncture video laparoscopy. The left pelvic sidewall mass near the left ureter was carefully resected and found to be endometriosis on final pathology. The vaginal cuff mass was also resected. Measurements and Main Results Pathology reported endometriosis juxtaposed with well-differentiated endometrioid adenocarcinoma. Immunohistochemical tumor staining further confirmed gynecological origin. Conclusion The relationship between endometriosis and ovarian cancer has been established, although not fully elucidated. Therefore, among patients with a history of endometriosis, continued regular gynecologic follow up is recommended not only for recurrence but also for possible malignant transformation. Presentation of unique case of postmenopausal patient with previous total hysterectomy, salpingo-oophorectomy and excision of endometriosis who developed cancer originating from endometriosis. Case report Endometriosis Referral center This video presents a 78-year-old G1P1 female with a history of endometriosis who presented with post-coital vaginal bleeding. She had a history of a total abdominal hysterectomy at the age of 46 due to pelvic pain, and later underwent bilateral salpingo-oophorectomy and excision of endometriosis at the age of 56 due to continued pain. She was on hormonal supplementation with transdermal estrogen. Preoperative examination and imaging revealed a 5 cm friable mass at the vaginal cuff and a smaller pelvic mass in the left pelvic sidewall. The patient underwent multi puncture video laparoscopy. The left pelvic sidewall mass near the left ureter was carefully resected and found to be endometriosis on final pathology. The vaginal cuff mass was also resected. Pathology reported endometriosis juxtaposed with well-differentiated endometrioid adenocarcinoma. Immunohistochemical tumor staining further confirmed gynecological origin. The relationship between endometriosis and ovarian cancer has been established, although not fully elucidated. Therefore, among patients with a history of endometriosis, continued regular gynecologic follow up is recommended not only for recurrence but also for possible malignant transformation.