Malignant transformation of endometriosis is a rare event. The ovaries are the most common sites reported in the literature. Postmenopausal cancer arising in extragenital endometriosis is still more exceptional. Hormone replacement therapy and perhaps, to a lesser extent, Tamoxifen could be risk factors for the malignant transformation of endometriosis. We herein report the case of a patient who has developed, after 11 years of hormone replacement therapy, an extragenital endometrioid carcinoma in the vesico-uterine pouch.