Between March 1978 and October 1983, 65 patients with locally advanced soft tissue sarcomas were treated at the cyclotron of Louvain-la-Neuve. 46 patients are analysed, 19 patients with intraabdominal or intrathoracic lesions are excluded. After "radical surgery" (no "gross tumour" present at the time of neutron therapy), a local control rate of 93% was achieved (25/27 patients) and the survival was 74%. In a second group of 19 patients with incompletely resected, or recurrent, or inoperable tumour, a local control was obtained in four cases (21%), and 13 patients were alive (69%). The follow-up ranged from three to 65 months (mean: 25,9 months). Ten severe complications were observed (22%); they were related to the field sizes, which reflected the local tumour extent.