FEV1 is considered an important parameter for asthma diagnosis and follow-up. However, it has been proposed that FEF25-75 could be more sensitive than FEV1 to detect slight airways obstruction. Bronchial reversibility defined by positive response to bronchodilation test. The aim of the present study was to define whether an impaired FEF25-75 value (less than 65 percent of predicted) may be predictive for reversibility in a large cohort of allergic children with rhinitis or asthma. Six hundred allergic children were recruited: 300 with controlled asthma and 300 with allergic rhinitis. All of them were evaluated by performing spirometry, bronchodilation test, and skin prick test. Two predictors were significantly associated with bronchial reversibility: i) an impaired FEF25-75 value (less than 65 percent of predicted), and ii) sensitization to perennial allergens. It was more relevant in children with rhinitis (ORAdj:8.9 and 2.2 respectively). In conclusion, this study, conducted in real life, could suggest that an impaired FEF25-75 value (less than 65 percent of predicted) may be considered a reliable marker of bronchial reversibility, mainly in children with allergic rhinitis.