From February 1968 to February 1988, 50 patients above 10 years of age with a soft tissue sarcoma were treated with interstitial brachytherapy, combined with a wide excision. After pathologic review, 48 were included in the final analysis. A pathological grading was made possible in 41, which showed a majority of high grades (2 + 3 = 86%). Patients presented mainly with small (less than 5 cm: 36) or mid-size lesions (greater than 5 cm: 12). The tumor was located in the limbs (32), trunk (9), and head and neck (7). Four patients had metastases at the time of treatment. Brachytherapy was part of the initial treatment in 22 cases, and of a salvage procedure after previous excision(s) combined or not with another form of treatment in 26. A uniform technique of iridium 192 wires after-loaded in plastic tubing was used. Sixty Gy median doses were delivered with brachytherapy alone (44) or combined with external beam (4). Sixteen patients also received an adjuvant chemotherapy. Follow up ranged from 16 months to 20 years (median 82 months). At the time of analysis, two patients (4%) only had failed in the irradiated volume, but the marginal failures rate (14:31%) was unexpectedly high. Seven of the patients who failed (43%) were salvaged by a second similar procedure. The 5-year survival was 62% in non-previously treated patients and 56.5% in previously treated ones (pNS). By multivariate analysis, only the tumor location appeared predictive of LF (p less than 0.01), which in turn was strongly correlated with the metastatic outcome (p less than 0.01). Necroses were observed in 17 cases (35%) and associated with a benign course in most of them. High dose brachytherapy combined with conservative surgery is highly effective in small and mid-size soft tissue sarcomas located in the extremities and head and neck, whereas in trunk and in recurrent tumors, the adjunction of large fields external radiotherapy and/or possibly polychemotherapy appears necessary.