Treatment of 158 patients with retroperitoneal sarcomas (1951--1977) resulted in a mean five-year survival of 40% (range 37--45%) after complete excision. Only 22% (range 19--25%) of the patients were free of disease. Survival for five years after incomplete excision was 3%. Operative mortality after complete excision declined from 21 to 2% during this period. Anatomical barriers to wide resection, high-grade histology, and local recurrence were the most important factors determining survival. The need for adjuvant therapy is emphasized by a 77% recurrence rate among patients with apparent complete excision. Brachytherapy (125Iodine, 192Iridium) afterloading techniques and supplemental external radiation are recommended to improve local control and chemotherapy is indicated to diminish the potential for metastatic spread. The contribution of adjuvant therapy after complete excision in this series was difficult to assess because of the number of uncontrolled variables, different histologic types, and limited number of patients treated by multimodality therapy. Although radiation and chemotherapy may be beneficial after incomplete resection, prolonged survival was only seen in patients with liposarcoma and low-grade fibrosarcoma.