The results of amputating an entire lower extremity with the corresponding half of the pelvis for malignant disease in 50 patients seen before the end of December, 1954, are reviewed for the purpose of assessing the therapeutic value of the operation and identifying the factors that affect immediate surgical mortality. No hospital deaths occurred, but in 1955 a hospital death followed operation. It resulted from pulmonary embolism on the seventh post-operative day. This extremely low mortality is ascribed to the relatively short duration of the operative procedure (which averaged 21/4 hours), to the general supportive care given to the patient, and to the replacement of lost blood. A tracheal tube was used by the anesthesiologist in every case. The surgeon must avoid seeding the wound with tumor cells, and transabdominal biopsies of tumors of the os coxae during exploratory laparotomy or through the incision made at the time of hemipelvectomy are strongly condemned. The life expectancy of the patient depended on the type of diseases that necessitated operation, and the best post-operative survival rate was in the group of patients with chondrosarcoma.