In this retrospective study, the results of postoperative neutron boost therapy for 40 soft tissue- and 18 chondrosarcomas are presented. In 65.5% and 34.5% of all cases, microscopic to macroscopic tumour residual was left postoperatively. Locally advanced and moderate to highly malignant tumours were found at surgery in 81% and 69%, respectively. Except for seven patients with a whole series of neutrons to 16 Gy, the other cases were treated with initially 40 to 50 Gy photons and a subsequent neutron boost of 4 to 6 Gy. The median follow-up was 29.3 and 36.2 months for the soft tissue- and chondrosarcomas. The actuarial three-year local control and overall survival rates were 69.3% and 91% for soft tissue- vs. 55.6% and 62.9% for chondrosarcomas. With regard to the extension of surgery (microscopic or macroscopic residual), local control rates of 80% and 60% for soft tissue- vs. 62.5% and 40% for chondrosarcomas were observed. The overall local failure rate was 32.8% with a median disease-free interval of ten respectively eleven months for soft tissue and chondrosarcomas. 17 out of 19 local recurrences were due to inadequate irradiation portals for the neutron boost or to insufficient total doses in the initially treated photon target volume.