Between 1954 and 1981, 72 patients with unresectable soft tissue sarcomas were treated with radiotherapy at The University of Texas M. D. Anderson Hospital and Tumor Institute at Houston, 57 with photons alone and 15 with neutrons for at least part of the treatment. Twenty-three patients received systemic chemotherapy in addition to radiation therapy. The absolute 2-year and actuarial 5-year tumor control rates were 39 and 29%, respectively. In this heterogeneous series, the malignancy group (based on pathologic diagnosis) was the only factor significantly affecting tumor control probability, which at 5 years was 58% for 12 patients with group I tumors, 32% for 10 patients with group II tumors, and 17% for 50 patients with group III tumors. No relationship between total dose and tumor control probability was found in this group of patients, though the duration of tumor control was longer in those receiving 65 Gy or more. No apparent improvement in tumor control was observed in the subsets of patients receiving fast neutron therapy or combined modality treatment with chemotherapy, but because of the many unmatched variables between the groups, no meaningful comparison of treatment modalities can be made. Distant metastasis were seen more frequently in higher malignancy groups, whereas size or site of tumors did not significantly influence the incidence of distant metastasis. Six patients sustained major complications of radiotherapy, of whom five received total doses in excess of 70 Gy or its estimated biologic equivalent.