OBJECTIVE Adjuvant radiotherapy (RT) has been shown to improve local control in patients with soft tissue sarcoma of the extremities (STS). The specific impact of adjuvant radiation on patients with positive margins, however, has not been clearly defined. The purpose of this study was to determine if adjuvant RT improves local control in patients with high-grade STS who had positive margins of resection. METHODS Between 8/82 and 2/97, 110 adult patients with primary high-grade STS of an extremity underwent limb sparing surgery and were found to have a histologically positive microscopic surgical margin. Ninety-one (83%) received RT and 19 (17%) had no RT. The two groups were balanced with regard to size, site, location, and tumor depth. Adjuvant RT was delivered with brachytherapy (BRT) alone in 34 patients, external beam radiotherapy (EBRT) alone in 33 patients, or BRT+EBRT in 24 patients. The BRT dose was 45 Gy when used alone and 15-20 Gy when used as a boost. The EBRT dose was 60-70 Gy when used alone and 45-50 Gy when given with BRT. The median follow-up time was 41 months (range, 3-186 months). RESULTS The overall 5 year local control rate was 71%. This rate was significantly higher in the RT group compared to the no RT group (74% vs. 56%, respectively) (p = 0.01). On univariate analysis, lower extremity site and proximal location were also found to be predictors of improved local control (p = 0.03 and 0.03, respectively). However, only proximal location and the use of RT retained their significance as predictors of improved local control on multivariate analysis (p = 0.003 and 0.01, respectively). The overall 5-year distant relapse-free survival, disease-free survival, and overall survival rates were 54%, 44%, and 53%, respectively. No statistical differences were found in these survival rates between RT and no RT groups. CONCLUSIONS Based on this study, adjuvant radiotherapy seems to improve local control in patients with high-grade STS of the extremity with positive margins. However, local recurrence still occurs in a substantial proportion of patients, mandating further need for improvement.