A 55-year-old woman, gravida 2 and para 2, started to take herbal compound medicine which contains black cohosh (Cimicifuga racemosa) and St. John`s wort (Hypericum perforatum) for hot flushing. She had adenomyosis and uterine myoma which had been followed every 6 months and showed no change. The result of cervical cytology had been normal. After 17 months, she presented with complaint of lower abdominal pain and voiding discomfort and Computer tomography (CT) imaging demonstrated a huge uterine mass with inhomogeneous pattern, about 12 x 12 x 15 cm in dimension (Fig. 1). The tumor marker profile was as follows: CA-125 (298.2 IU/mL; normal <35 IU/ml), CA 19-9 (39.6 IU/mL; normal <37 IU/mL), carcinoembryonic antigen (1.9 ng/mL; normal <5 ng/mL). From these findings, huge uterine myoma with secondary degeneration or leiomyosarcoma was suspected. At laparotomy, multiple friable tissues on uterine surface were seen and the posterior wall of the uterus was densely adhered to the rectosigmoid colon. The patient had a total hysterectomy, bilateral salpingoophorectomy, right hemicolectomy and reanastomosis. The final pathological study revealed grade 1 endometrioid adenocarcinoma arising in adenomyosis, with direct invasion of the muscle layer of the colon but with no involvement of the endometrium and cervix of uterus (Fig. 2). The cytology of ascites suggested the presence of adenocarcinoma. Postoperatively, radiation therapy to the pelvis and chemotherapy were administered.