The different role of prenatal and postnatal exposure to tobacco smoke in respiratory outcomes in infants has not yet been clearly established. Our objective is to assess the effects of these exposures on the risk of respiratory outcomes during the first year of life of infants from a Spanish multicenter cohort study2506 women were monitored until delivery. 2039 infants made up the final population. The outcomes were the occurrence of: otitis, cough persisting for more than three weeks, lower respiratory tract symptoms (wheezing or chestiness), and lower respiratory tract infections (bronchitis, bronchiolitis or pneumonia). The relationship between prenatal and postnatal exposure and health outcomes was explored using logistic regression analysisMaternal smoking during pregnancy increased the odds for wheezing (OR: 1.41, 95% CI: 0.99 - 2.01) and chestiness (OR: 1.46, 95% CI: 1.03 - 2.01). Postnatal exposure from fathers was associated with otitis (OR: 1.25, 95% CI: 1.01-1.54). Passive exposure at work of non smoking mothers during pregnancy was related to cough (OR: 1.62, 95% CI: 1.05 - 2.51)Conclusions: Exposure to tobacco smoke was related to a higher risk of experiencing respiratory outcomes in young infants. Prenatal exposure was that most clearly associated with the respiratory outcomes analyzedThis article is protected by copyright. All rights reserved.