Surgical treatment of pelvic tumors, especially malignant tumors, is difficult for several reasons. First, in many cases there are no symptoms until the tumor has grown to a large size. Surgeons frequently encounter a massive chondrosarcoma, giant cell tumor, or chordoma of the pelvis. In such cases of tumors with extended growth, a wide margin can seldom be obtained because of the anatomy of the pelvis. Second, orthopedic surgeons, in general, are not familiar with the anatomy of the vessels and nerves in the pelvic cavity. In addition, pelvic tumors are relatively rare, and orthopedic surgeons do not have many opportunities to become skilled in pelvic tumor surgery. Massive bleeding of over 5000 ml is often encountered, and the operative time is usually very long. Third, a histological diagnosis is difficult because often a biopsy specimen cannot easily be obtained. Open biopsy often leads to contamination of the tumor tissue, massive bleeding, or unnecessary free flaps.