Allergic rhinitis and asthma are closely associated. Bronchial hyperreactivity (BHR) is a pathophysiological characteristic of asthma. Forced expiratory flow between 25 and 75% of vital capacity (FEF(25-75)) has been previously shown to be able to predict BHR in adult patients with allergic rhinitis. Therefore, the aim of this study was (i) to evaluate the presence of BHR in a large group of children with allergic rhinitis, asthma or both and (ii) to confirm whether FEF(25-75) might be related to BHR and may predict BHR also in a pediatric population. Nine hundred fifty children with allergic rhinitis (350), asthma (300), or both (300) were enrolled. Clinical examination, skin-prick test, spirometry, and methacholine challenge were performed in all patients. Severe BHR was quite frequent in allergic children, mainly in asthmatic patients. FEF(25-75) values were significantly related to BHR grade, mainly in children with rhinitis (r = 0.69). Impaired FEF(25-75) values (such as ≤65% of predicted) constituted a relevant predictive factor for severe BHR, mainly in children with rhinitis (odds ratio, 8.9). In conclusion, this pediatric study confirmed that impaired FEF(25-75) values might predict severe BHR in children, mainly in those with allergic rhinitis. Therefore, low FEF(25-75) values could suggest BHR in children.