<h3>History</h3> An 81-year-old woman was admitted to the hospital with a complaint of weakness and constipation. Her temperature was 38.7 °C and her WBC count was 38,300/cu mm. Physical examination suggested the presence of a large pelvic tumor. An abdominal roentgenogram showed a large, spheroid, radiolucent mass, extending from the pelvis into the lower abdomen (Fig 1). <h3>Diagnosis</h3> Squamous cell carcinoma arising in benign ovarian cystic teratoma, with fistulous communication to the sigmoid colon. A barium enema (Fig 2) showed passage of barium into the radiolucent mass. The patient underwent a resection of the pelvic mass and sigmoid colon, colostomy, hysterectomy, and bilateral salpingo-oophorectomy. The tumor was dumbbell-shaped, with a small solid portion containing a few teeth and a large gas-filled portion. The latter was lined by squamous cell carcinoma, which was also present in the fistulous communication to the sigmoid. The patient's postoperative course was complicated by cardiac arrhythmia