Since 1927, 130 patients with well-documented malignant fibrous histiocytoma of bone have been diagnosed and treated at Memorial Hospital for Cancer and Allied Diseases. This sarcoma is 10 times less frequent than osteogenic sarcoma in this hospital. It most commonly occurred spontaneously (72%), whereas in the rest (28%) it followed previous radiation or various pre-existent osseous conditions, most often Paget's disease. The appendicular skeleton was the commonest site of involvement. The majority of the patients were middle-aged or older adults with a mean of 40.5 years of age; only 21.5% were 21 years or younger. Histologically, the lesions were subclassified as fibrous (62%), histiocytic or xanthomatous (30%), and malignant giant cell tumor (8%) variants. Older patients were more likely to have a secondary malignant fibrous histiocytoma, especially following radiation or Paget's disease. Overall survival estimates at 2 years and 5 years were 71% and 53%, respectively. Survival was not dependent on the histologic subtype of the lesion, but was strongly influenced by the histologic grade of malignancy. Important prognostic factors were the age of the patients and whether the lesions were primary de novo or secondary sarcomas: the older patients and those with secondary lesions did substantially worse.