Primary soft tissue sarcoma of the retroperitoneum is a rare disease. A series of 11 evaluable adult patients with retroperitoneal soft tissue sarcomas is reported. These patients were treated with complete surgery and adjuvant radiation therapy (total dose from 50 to 64 Gy) using an 18 MeV linear accelerator. After a median follow-up of 48 months (range, 6-84), 4 patients had a local-regional recurrence, 3 had distant metastases, and 4 died of progressive disease. Four-year estimated disease-free survival was 54.5% and overall survival was 70%. Treatment was well tolerated by most patients: 7 patients experienced moderate gastrointestinal toxicity, mainly nausea and diarrhea, during radiotherapy; 2 cases had weight loss > 15% at the end of the therapy; and chronic ileitis was observed in 2 cases. We conclude that adjuvant radiotherapy seems to reduce the incidence of local-regional recurrences in these patients. No radiation-induced irreversible injury was observed, but one young woman had amenorrhea after radiotherapy. Controlled clinical trials are warranted to define the role and effectiveness of adjuvant radiotherapy and/or chemotherapy in retroperitoneal soft tissue sarcomas.