=Chorio-epithelioma= or =syncytioma malignum= is a rare and peculiar malignant growth of the uterus which occurs after pregnancy. It originates at the placental site from the epithelial cells covering the chorionic villi. It occurs during the course or after the termination of a uterine or tubal pregnancy. In typical cases the disease immediately follows labor at term, abortion, or a destroyed extra-uterine pregnancy. It may, however, remain latent for weeks or months. The tumor may be a nodular or pedunculated outgrowth attached to the uterine wall; a fungoid growth from the endometrium; or an intramural growth covered with endometrium. The tumor varies in size from that of a cherry-stone to a mass several inches in diameter. It is composed of soft fragile spongy tissue, light or dark red in color, infiltrated with blood, and containing circumscribed hemorrhages. Histologically the tumor consists of many types of cells irregularly placed; syncytial tissue, cells derived from Langhans’ layer, and sometimes chorionic connective tissue. There are numerous cavities containing blood and connective tissue. Metastatic growths have a similar structure. Metastasis takes place through the vascular system and may reach distant organs--the lungs, liver, and spleen. _Symptoms._--There is no characteristic symptom of chorio-epithelioma. The chief symptom is irregular or continuous hemorrhage from the uterus following a labor, an abortion, or an extra-uterine pregnancy. The body of the uterus is enlarged, and the cervical canal dilated as in cancer and sarcoma. A positive diagnosis can be made only by microscopic examination of tissue removed by the curet. _Treatment._--As the disease is exceedingly malignant and of rapid growth, immediate hysterectomy is indicated. CHAPTER XX. FIBROID TUMORS OF THE UTERUS. Fibroid tumors originate in the muscular wall of the uterus. They are composed of elements resembling, to a greater or less extent, those that compose the middle uterine wall. They consist of connective tissue and of unstriped muscular tissue in varying proportions. Uterine tumors composed exclusively of muscular fibres--true myomata--very rarely occur. A number of names, based upon the proportion of the component elements, have been used by writers to designate these tumors. They have been called fibroma, myoma, myo-fibroma, and fibro-myoma. The natural history of all the varieties is about the same, and varies but little with the proportion of the elements. I shall therefore consider them under the general name of fibroid tumors of the uterus. Fibroid tumors of the uterus are benign, in the sense that they do not, like cancer, infiltrate contiguous structures or infect the general system.