Associations between maternal smoking during pregnancy () or any secondhand smoke (SHS) during infancy () and prevalence of asthma up to 14–16 y of age in five European birth cohorts. Cohort-specific odds ratios (ORs) and 95% confidence intervals (CIs) were obtained by generalized estimating equation models. Adjusted for sex, parental education level, parental allergy, older siblings, breastfeeding, study center, intervention arm, and early day-care attendance. Combined OR and 95% CI were derived from cohort-specific OR and 95% CI using a random effects model. Note: BAMSE, Children, Allergy, Milieu, Stockholm, Epidemiology; GINIplus, German Infant Nutritional Intervention; LISA, Influences of Lifestyle-Related Factors on the Immune System and the Development of Allergies in Childhood; MAS, Multicentre Allergy Study; PIAMA, Prevention and Incidence of Asthma and Mite Allergy.