Malignant fibrous histiocytoma of soft tissue. A population-based epidemiologic and prognostic study of 137 patients. Epidemiology and prognosis were analyzed in a consecutive, population-based series of 137 patients with malignant fibrous histiocytoma of soft tissue in the extremities and trunk wall, with a complete follow-up of minimum 3 years. All but one patient were treated by surgery in 28 cases combined with adjuvant radiotherapy or chemotherapy. The annual incidence was 0.42/10(5). The ratio men to women was 1.1. The median age was 64 years (range, 22 to 87 years). The thigh was the most common location. The median size was 6 cm. Superficial tumors constituted 43% and were smaller than deep-seated tumors. Eighty-three tumors were storiform-pleomorphic, 53 were myxoid, and one was of inflammatory type. The myxoid tumors were smaller and more often superficial. The cumulative 5-year survival rate for all patients was 0.7, but differed markedly between the histologic types; it was 1.0 in patients with myxoid tumors and 0.5 in patients with storiform-pleomorphic tumors. In the 77 patients with storiform-pleomorphic tumors without metastases at presentation, only tumor size larger than 10 cm and tumor necrosis independently impaired survival. The 23 patients who had none of these risk factors had a 5-year survival rate of 0.8. 