BACKGROUND AND OBJECTIVE: Exposure to environmental tobacco smoke (ETS) is associated with impaired lung function in childhood, which in turn, is associated with chronic obstructive pulmonary disease (COPD) in adulthood. However, little is known regarding the direct association between childhood exposure to ETS and the development of COPD. The main objective of the present study was to examine the associations between childhood ETS exposure and adult COPD and respiratory symptoms. METHODS: Patients with COPD (n = 433) and control subjects (n = 325) participated in the Bergen COPD Cohort Study during 2006-2009. Participants performed spirometry and answered extensive questionnaires. The risk factors for COPD, morning cough, cough with phlegm, chronic cough and dyspnoea were examined using logistic regression analysis. Analyses were stratified by gender. RESULTS: The prevalence of childhood exposure to ETS was 61%. After adjustment, women who were exposed to ETS during childhood had a higher risk of COPD than those who were not exposed: odds ratio 1.9, 95% confidence interval 1.0, 3.7. Other important predictors for COPD and respiratory symptoms among women were occupational dust exposure (COPD), family history of COPD (COPD, all symptoms), current exposure to ETS in the home (morning cough) and education (COPD, dyspnoea). ETS exposure during childhood was associated with respiratory symptoms among males (odds ratios 1.5-1.7). Risk factors for COPD among men were occupational dust exposure, family history of COPD and level of education. Occupational dust exposure and family history of COPD also predicted dyspnoea among males. CONCLUSIONS: Exposure to ETS during childhood was associated with COPD and respiratory symptoms in adulthood. Although active smoking is still the most important risk factor for COPD, reduction of childhood ETS exposure could contribute to the prevention of COPD and respiratory symptoms.