As part of a collaborative study of risk factors for childhood brain tumours, the effects of the mother's smoking and her potential for passive smoking exposure during the pregnancy were assessed in a case-control study. Parents of 91 cases and 321 population controls from Northern Italy, matched for age, sex and residence, were interviewed about their lifetime smoking habits. Mother's smoking during pregnancy was associated with an odds ratio (OR) of 1.7 (95% CI 0.8, 3.8) of brain tumour in her child although this was not statistically significant. Among non-smoking mothers, the risk for light and heavy exposure to passive smoking was 1.7 (0.8, 3.6) and 2.2 (1.1, 4.5) respectively, and a statistically significant dose-response relationship was found (p trend = 0.02). These results must be interpreted within the constraints of the relatively small sample size and the likely misclassification produced by the difference between the potential for exposure to passive smoke and the true exposure. However, they add another piece of information to the growing body of evidence available about the health consequences both of active and of passive smoking and highlight the need for more information about this putative association.