A case of androgen-secreting borderline endometrioid tumor arising in endom
etriosis of the rectovaginal septum is presented. It occurred 10 years afte
r total abdominal hysterectomy and bilateral salpingo-oophorectomy for exte
nsive endometriosis of the fallopian tubes and ovaries, adenomyosis, and le
iomyomas of the uterus. We believe 7 years of unopposed continuous oral est
rogen replacement therapy contributed to the malignant transformation of th
e endometriosis.