Data from a large, population-based, case-control study were analyzed to assess the role of parental smoking in childhood brain tumors. Parents of 361 cases, newly diagnosed between January 1, 1977 and December 31, 1981 and ascertained from eight Surveillance, Epidemiology, and End Results (SEER) program registries, and 1,083 controls had been interviewed. No significant differences in risks were found to be associated with maternal or paternal smoking at any time (odds ratio (OR) = 0.92 for mothers and 1.06 for fathers), during the year of birth of the child (which included both the prenatal and postnatal periods) (ORs = 0.84 for < 1 pack/day and 1.0 for > or = 1 pack/day for mothers, and 0.68 for < 1 pack/day and 1.07 for > or = 1 pack/day for fathers), or 2 years before the child was born, i.e., the pre-conception period (ORs = 0.75 for < 1 pack/day and 1.01 for > or = 1 pack/day for mothers, and 0.90 for < 1 pack/day and 1.15 for > or = 1 pack/day for fathers). Mothers were also specifically asked if they smoked during the pregnancy, and no association was found compared with never smokers (OR = 1.08, 95% confidence interval (CI) 0.80-1.45) or for ever-smokers who continued to smoke during pregnancy compared with those who stopped smoking during pregnancy (OR = 1.15, 95% CI 0.75-1.78). Finally, no significant increase in risk of brain tumors was found for the child's passive exposure to parental smoking during the period from birth to diagnosis of the brain tumor in the case. The lack of an effect of parental smoking was observed for both the major histologic types and locations of brain tumors. These findings and those from earlier studies provide no support for the hypothesis that parental cigarette smoking influences the risk of brain tumors in children.