Background or purpose. A joint analysis of data from three contributing centres within the intraoperative electron-beam radiation therapy (IOERT) Spanish program was performed to investigate the main contributions of IORT to the multidisciplinary treatment of high-risk extremity soft tissue sarcoma (STS). Methods and materials. Patients with an histologic diagnosis of primary extremity STS, with absence of distant metastases, undergoing limb-sparing surgery with radical intent, external beam radiotherapy (median dose 45 Gy) and IOERT (median dose 12.5 Gy) were considered eligible for participation in this study. Results. From 1986-2012, a total of 159 patients were analysed in the study from three Spanish institutions. With a median follow-up time of 53 months (range 4-316 years), 5-year local control (LC) was 82 %. The 5-year IOERT in-field control, disease-free survival (DFS) and overall survival (OS) were 86, 62 and 72 %, respectively. On multivariate analysis, only microscopically involved margin (R1) resection status retained significance in relation to LC (HR 5.20, p < 0.001). With regard to IOERT in-field control, incomplete resection (HR 4.88, p = 0.001) and higher IOERT dose (>= 12.5 Gy; HR 0.32, p = 0.02) retained a significant association in multivariate analysis. Conclusion. From this joint analysis emerges the fact that an IOERT dose >= 12.5 Gy increases the rate of IOERT in-field control, but DFS remains modest, given the high risk of distant metastases. Intensified local treatment needs to be tested in the context of more efficient concurrent, neo- and adjuvant systemic therapy.