Malignant (fibrous) histiocytoma is currently defined as a malignant primary bone tumor that contains a mixture of fibrogenic cells and cells that are histologically similar but which appear to be histiocytic. In this type of histiocytoma the nuclei are often indented; cytoplasm is usually abundant and may be slightly foamy; nucleoli are often large; and multinucleated malignant cells are usually a prominent feature. Many dedifferentiated chondrosarcomas, osteosarcomas, and fibrosarcomas of bone contain areas that resemble what we regard as malignant (fibrous) histiocytoma. When the entirety of a malignant tumor of bone fits the outlined histologic pattern, the designation of malignant (fibrous) histiocytoma seems appropriate. From 158 fibrosarcomas of bone and 962 osteosarcomas of bone in our files, 35 tumors were segregated because they appeared to be properly designated as malignant (fibrous) histiocytoma. A wide age range was represented by affected patients, and a large variety of bones harbored these tumors. Approximately one-third of patients eligible for 5-year follow-up were long-term, symptom-free survivors. Four deaths occurred from the tumor after more than 5 years, and one patient had radiographic evidence of pulmonary metastasis 7 years after amputation. Radiation therapy has been curative in at least two cases. The correct designation for these tumors in the light of current knowledge is malignant tumor, consistent with malignant (fibrous) histiocytoma.