Of 229 patients with primary Ewing's sarcoma of bone, thirty-seven survived five years or longer. When the patients who survived five years or longer were compared with the 192 who did not, two factors associated with longer survival were identified in this retrospective study: location of the primary tumor within an extremity and inclusion of surgery as part of the initial treatment. The probability of five-year survival for all 229 patients with primary Ewing's sarcoma was 16 per cent. For those seen since 1950, this probability was 18 per cent, and for patients without metastasis, it was 22 per cent.