Background: Early exposure to parental smoking appears to influence the development of the airways and predispose to respiratory symptoms. A study was undertaken to determine whether the consequences of parental smoking could be traced in adulthood. Methods: Information from interviewer-led questionnaires was available for 18 922 subjects aged 20–44 years from random population samples in 37 areas participating in the European Community Respiratory Health Survey. Lung function data were available for 15 901 subjects. Results: In men, father's smoking in childhood was associated with more respiratory symptoms (ORwheeze 1.13 (95% CI 1.00 to 1.28); never smokers: ORwheeze 1.21 (95% CI 0.96 to 1.50)) and there was a dose-dependent association between number of parents smoking and wheeze (one: OR 1.08 (95% CI 0.94 to 1.24); both: OR 1.24 (95% CI 1.05 to 1.47); ptrend = 0.010). A reduced ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) was related to father's smoking (-0.3% (95% CI -0.6 to 0)) and number of parents smoking (ptrend <0.001) among men. In women, mother's smoking was associated with more respiratory symptoms and poorer lung function (ORwheeze 1.15 (95% CI 1.01 to 1.31), never smokers: ORwheeze 1.21 (95% CI 0.98–1.51); FEV1 -24 ml (95% CI -45 to -3); FEV1/FVC ratio -0.6% (95% CI -0.9 to -0.3)). These effects were possibly accounted for by maternal smoking in pregnancy (ORwheeze 1.39 (95% CI 1.17 to 1.65); FEV1 -23 ml (95% CI -52 to 7); FEV1/FVC ratio -0.9% (95% CI -1.3 to -0.4)) as there was no association with paternal smoking among women (interaction by sex, p<0.05). These results were homogeneous across centres. Conclusion: Both intrauterine and environmental exposure to parental tobacco smoking was related to more respiratory symptoms and poorer lung function in adulthood in this multicultural study. The age window of particular vulnerability appeared to differ by sex, postnatal exposure being important only in men and a role for prenatal exposure being more evident in women.