31 patients with primary Ewing's sarcoma of the ribs were treated according to the protocols of CESS 81, CESS 86P and CESS 86. The results of treatment were reviewed and analysed. 24 patients presented with localised disease and 7 with regional disease. 20 of 24 localised cases and 6 of 7 regional cases underwent tumour resection. All but 2 localised cases received irradiation. The cumulative relapse-free survival (RFS) rate of 31 patients was 61% at 12.8 years. Patients with poor prognosis had tumour of the upper ribs (P = 0.0338), the posterior component of the ribs (P = 0.0597), or regional disease (P = 0.0001). Tumour size, existence of pleural effusion, type of the surgical margin and response to chemotherapy were not significant prognostic factors. Most of the localised cases could be controlled by combined treatment, but in regional cases prognosis remained poor.