BACKGROUND To evaluate outcome and prognostic factors in Saudi Arabian patients with metastatic Ewing sarcoma and PNET of bone (PMES) at diagnosis. PROCEDURE Ninety-nine of 304 (33%) consecutive patients with Ewing sarcoma and PNET of bone registered at our centre from 1975 to 1998, had metastatic disease at registration and 93 were available for analysis. The maximum x-axis diameter of the primary tumor was used as the measure of primary tumor size. Usually a trial of systemic treatment was undertaken before a decision was made on local treatment. Standard chemotherapy regimens were used in all treated patients. Forty-one (44%) patients did not receive radical local treatment due to an inadequate response to chemotherapy, or a decision not to undertake more than palliative treatment. Radical treatment of the primary site was radiation alone 41 (79%), resection alone 7 (13%), and resection and radiation 4 (8%). RESULTS The 5-year survival rates were 9% for all 93 evaluable patients, 16% for 52 patients who received chemotherapy and radical local treatment, 0% for 41 patients who received lesser treatment, 19% for 43 patients with lung metastases alone, and 0% (P = 0.002) for 50 patients with other sites involved. For 60 patients with imaging data, 5-year survivals were 34 and 0% when the maximum transverse diameter of the primary tumor was < 10 cm (N = 20) and > or = 10 cm (N = 40), respectively. CONCLUSIONS Small primary tumor size and the presence of lung metastases alone were the only significant favorable prognostic factors. Earlier diagnosis will be the basis for better results.