In a case-control study of childhood rhabdomyosarcoma (RMS), families of 33 cases and 99 controls were interviewed. A relative risk (RR) of 3.9 was found associated with fathers' (but not mothers') cigarette smoking (P = 0.003). Cases had had fewer immunizations than controls, particularly smallpox vaccination (RR = 0.2; P = 0.001), and conversely had more preventable infections. An RR of 3.2 (P = 0.03) was found associated with exposure to chemicals and and RR of 3.7 (P = 0.004) was found associated with diets that included organ meats. Mothers of cases were more likely to be over age 30 years at subject's birth, to have used antibiotics preceding or during pregnancy, and to have had an overdue and/or assisted delivery. Other findings suggest that low socioeconomic status is associated with an increased risk of RMS. These aggregate findings imply that environmental factors may play an important role in the etiology of childhood RMS.