Aims : To describe the recent epidemiological knowledge that permits the wheezing phenotypes in preschool children to be distinguished more precisely, provide updated information about the specific risk factors for persistence of asthma into school age, describe the roles that allergy and bacterial infections play in the development of wheezing in preschool children, review the controversy regarding antibiotic use in early childhood and its association with the development of asthma and describe the latest recommendations of the ERS task force on preschool wheeze.