1. A complete perusal of the literature revealed twenty cases of primary liposarcoma of bone acceptable as such to the authors. These were tabulated as to location and age. 2. Eight cases of osteo-liposarcoma, primary in bone, were encountered in the literature and an additional case was reported by the authors. 3. The authors described for the first time in the literature a new primary tumor of bone of mixed origin: osteo-rhabdomyosarcoma. After careful perusal of the literature they added three additional cases: two cases, previously reported as primary rhabdomyosarcoma of bone, which on careful evaluation of the radiographs in said publications and the paucity of microphotographs they considered to be osteo-rhabdomyosarcomas, and the other case, previously reported as malignant mesenchymoma of the sternum following radiotherapy for breast cancer. 4. The authors prefer to classify these tumors (osteo-liposarcoma and osteo-rhabdomyosarcoma) as "Tumors of Mixed Origin" and not as "Malignant Mesenchymomas". 5. A complete review of the literature revealed 219 reported "dedifferentiated" chondrosarcomas, or chondrosarcomas "with additional mesenchymal component", among which only nine (9) contained a bona fide rhabdomyosarcomatous component. The rest exhibited other mesenchymal tumors as osteogenic sarcoma, fibrosarcoma, malignant fibrous histiocytoma, angiosarcoma, and undifferentiated sarcoma. The authors recommend to continue classifying these tumors as chondrosarcomas with additional mesenchymal component or even as "dedifferentiated" chondrosarcomas but not as malignant mesenchymomas.