It is difficult to make a definitive diagnosis of asthma in preschool wheezing children, but because more than 80% of asthma begins before the age of 3 years and pulmonary impairment begins in preschool, it is necessary to identify children with preschool wheezing who are likely to develop persistent asthma. Studies have shown that the bronchial epithelial reticular basement membrane is significantly thicker and eosinophils are detectable in children with confirmed wheezing compared to control children without wheezing, indicating that airway remodeling and inflammatory responses are already present in children with wheezing. Without early intervention in children with wheezing, this can lead to reduced lung function and increased risk of asthma in adulthood. How can children with asthma be identified and diagnosed early? The Canadian Thoracic Society and Canadian Paediatric Society 2015 Diagnosis and Management of Asthma in Infants and Children states that asthma can be diagnosed in children under 5 years of age with more than 2 previous recurrent asthma-like symptoms and improvement after physician application of bronchodilators. 2015 GINA also states that asthma can be considered in patients with recurrent asthma-like attacks for whom anti-asthmatic therapy is effective. There are different phenotypes of asthma in infants and children, and their prognosis varies from phenotype to phenotype, as does the duration of treatment. Studies have shown that the Asthma Predictive Index (API) is effective in predicting the risk of developing persistent asthma in wheezing children within 3 years of age. Clinicians can use a positive API to identify children at high risk for asthma and to educate parents of affected children about the importance of asthma maintenance therapy.