[en] Purpose: Adjuvant radiotherapy has during the past decades become increasingly used in the treatment of localized soft tissue sarcoma. We evaluated the effect of radiotherapy (RT) on local recurrence rates (LRRs) in Scandinavia between 1986 and 2005. Methods and Materials: A total of 1,093 adult patients with extremity or trunk wall soft tissue sarcoma treated at four Scandinavian sarcoma centers were stratified according to the treatment period (1986-1991, 1992-1997, and 1998-2005). The use of adjuvant RT, quality of the surgical margin, interval between surgery and RT, and LRR were analyzed. The median follow-up was 5 years. Results: The use of RT (77% treated postoperatively) increased from 28% to 53%, and the 5-year LRR decreased from 27% to 15%. The rate of wide surgical margins did not increase. The risk factors for local recurrence were histologic high-grade malignancy (hazard ratio [HR], 5), an intralesional (HR, 6) or marginal (HR, 3) surgical margin, and no RT (HR, 3). The effect of RT on the LRR was also significant after a wide margin resection and in low-grade malignant tumors. The LRR was the same after preoperative and postoperative RT. The median interval from surgery to the start of RT was 7 weeks, and 98% started RT within 4 months. The LRR was the same in patients who started treatment before and after 7 weeks. Conclusion: The results of our study have shown that adjuvant RT effectively prevents local recurrence in soft tissue sarcoma, irrespective of the tumor depth, malignancy grade, and surgical margin status. The effect was most pronounced in deep-seated, high-grade tumors, even when removed with a wide surgical margin