Background: Subjects with allergic rhinitis (AR) suffer from impaired lung function, especially decreased FEF25-75%. The purpose of this study was to examine lung function and the long-term response to INCS in AR patients with impaired lung function, and to characterize the phenotype of these children. Methods: Two hundred two children with AR underwent an allergy evaluation including a skin prick test and spirometry. Children with impaired lung function were treated with daily nasal corticosteroids spray (INCS) and antihistamine as needed. Results: Fifty-three children out of 202 (26.3%) had impaired lung function: 34 of them (64.2%) had FEF25-75% values under 80% of predicted and normal FEV1 values, and 19 individuals (35.8%), had both FEF25-75% and FEV1 values below 80% of predicted. A positive correlation between FEV1 and FEF25-75% values (r=0.369, P=0.007) and a reverse correlation between duration of nasal symptoms and FEF25-75% values (r =-0.364, P= 0.012) were found. Post-ronchodilation FEV1 levels increased from 81.9 +/- 8.0 to 87.7 +/- 10.4 (P< 0.0001). Thirty-five of the 53 children complied with a continuous INCS treatment regimen over a period of 3-12 months, demonstrated increased FEF25-75% (84.4 +/- 13.6 vs. 70.1 +/- 7.1, P< 0.001) and FEV1 (92.3 +/- 10.9 vs. 84.4 +/- 7.8, P< 0.0001) after INCS treatment. However, FEF25-75% values were still significantly lower compared to the group of AR children with normal lung function (84.4 +/- 13.6 vs. 95.7 +/- 8.8, P< 0.0001). Conclusions: INCS improve FEF25-75% above 80% of predicted values in 2/3 of children with abnormal lung function. However, this improvement does not reach levels of AR children with normal lung function. (C) 2013 Wiley Periodicals, Inc.