The relationship between status of the surgical margin and local control of soft tissue sarcoma of the extremities by preoperative radiation therapy has been assessed in 132 consecutive patients from 1974 to 1988. The 5-year actuarial local control rate was 94% for all patients; the rates were 97% and 82% for the 104 tumors with negative margins and the 28 tumors with positive margins, respectively. The local control rate was independent of the extent of the negative margin. For primary sarcomas, the local control rates were 96%, 97%, and loo%, respectively, for margins that were negative at S 1 mm or > 1 mm, or the specimens were negative for tumor; for positive margins the result was 83%. The overall local control rate was lower (not significant) for recurrent than for primary sarcomas: 88% vs. 94%. On the other hand, when stratifying by margin status, no difference was observed in local control results, i.e.: (1) 97% and 91% for primary and recurrent tumors with negative margins, respectively, and (2) 83% and 80% for primary and recurrent tumors with positive margins, respectively. Local control was not significantly higher in those patients who were treated by surgical resection (S), radiation (RT), and re-excision of the previous tumor bed than in those whose radiation therapy was started after the biopsy and followed by one surgical resection. For primary sarcomas that were resected with negative margins the results were: 100% of 15 patients treated by S-RT-S and 96% of 75 patients treated by RT-S.