The results of fast neutron therapy of soft tissue sarcoma at the cyclotron of Louvain-la-Neuve are reviewed. 75 patients were analysed, the follow-up ranged from six to 102 months (mean: 30.7 months). 47 patients were treated after radical surgery. A local control rate of 91.5% (43/47) was achieved, and 70% of the patients are alive. 28 patients were irradiated with gross tumour present at the time of neutron therapy (recurrence, incomplete resection, inoperable): a local control was achieved in 5/28 cases (18%), and 68% of the patients are alive. A complication rate of 16% was recorded which was directly related to the treatment volume.