A study was made of the clinical course of 102 cases of fibrosarcoma of long bones. Of these, 55 were predominantly fibroblastic or pure fibrosarcomata while 47 contained extensive areas resembling so-called malignant fibrous histiocytoma (MFH). Treatment was similar in the two groups, and the five-year survival was the same, 34%, in both groups. Lung metastases developed in 63% of the fibroblastic sarcomata and 59% of the MFH-like tumours. Our study indicates that there is no significant difference in behaviour in fibrosarcoma with or without marked MFH features. The histological grading of both groups of fibrosarcomata together was of prognostic value; five-year survival was 64% in 14 Grade I tumours, 41% in 32 Grade II tumours and 23% in 56 Grade III tumours.