To determine risk factors for Ewing's bone sarcoma, the authors interviewed mothers of 43 patients diagnosed between January 1978 and August 1986 and 193 controls in the San Francisco Bay Area, California, regarding medical and occupational history of parents and other factors related to the subjects and their immediate families. Controls were selected by using random digit dial telephone methods. Adjusted relative risk estimates suggest that risks were elevated for children whose fathers were engaged in agricultural occupations during the period from 6 months prior to conception of the subject up to the time of diagnosis for the patients or interview for the controls (relative risk (RR) = 8.8, 95% confidence interval (CI) 1.8-42.7) and for children whose fathers had occupational exposure to herbicides, pesticides, or fertilizers (RR = 6.1, 95% CI 1.7-21.9, p = 0.002). Prior ingestion of poison or an overdose of medication was more common in patients than in controls (RR = 4.4, 95% CI 1.4-13.5). These and other findings should be investigated in larger population-based studies to determine specific factors that may account for the associations.