568 patients with localized Ewing sarcoma were randomized to receive alternating cycles of vincristine - doxorubicin - cyclophosphamide and ifosfamide-etoposide chemotherapy either every 14 or 21 days. Between cycles patients were administered filgrastim and at week 13 all patients received primary tumour treatment. The purpose of this study was to determine whether interval compression was effective in improving the prognosis of patients. At 5.5 years, results indicated that chemotherapy administered every 14 days was more effective than every 21 days, as it significantly increased the event-free survival rate without increasing toxicity.