Objective: latest the hypothesis that consuming Mediterranean diet and using olive oil for cooking/dressing salads during pregnancy might be associated with less wheezing during the first year of the offspring's life. Methods: A study was conducted in 1,409 infants (mean age, 16.6 +/- 2.5 months) attending healthy infant clinics in Spain. Dietary data of mothers' intake during pregnancy was collected by means of a parental food frequency questionnaire. Demographic information and data on wheezing during the first year of the offspring's life were also recorded. Infants were stratified according to any wheezing (42.2%) during the first year of life. Results: In the univariate analysis, adherence to a Mediterranean diet and using olive oil for cooking/dressing salads during pregnancy were both significantly associated with less wheezing during the first year of life. However, after multivariate analysis, only olive oil consumption during pregnancy remained associated with less wheezing in the studied period (aOR = 0.57 [95% CI = 0.4-0.9]); whereas male gender (1.8 [1.4-2.3]), day care attendance (2.15 [1.5-3.1]), maternal asthma (2.16 [1.3-3.6]), maternal smoking during pregnancy (1.83 [1.3-2.2]), infant eczema (1.95 [1.3-2.9]), and mould stains on the household walls (1.72 [1.2-2.5]) remained associated with wheezing. Conclusion: Our findings suggest a protective effect (primary prevention) of olive oil use during pregnancy on wheezing during the first year of the offspring's life. Pediatr Pulmonol. 2010; 45:395-402. (C) 2010 Wiley-Liss, Inc.