Increased levels of exhaled nitric oxide (FeNO) and airway hyperresponsiveness (AHR) to inhaled mannitol are related to allergic inflammation characterized by eosinophil infiltration and a clinical response to treatment with anti-inflammatory agents in subjects with asthma. This study determines the diagnostic accuracy of FeNO using absolute and normalized values to predict the presence of AHR to inhaled mannitol in an unselected population. Levels of FeNO and AHR to inhaled, dry-powder mannitol was measured in 180 unselected, steroid-naïve, non-smoking adolescents and young adults. The area under the curve for the receiver operating characteristics curve for FeNO to identify a positive response to mannitol was 91.9% (CI95: 87.7-96.2). The optimal cut-off was 25 ppb (185% predicted) and a sensitivity of 100% (CI95: 83.9-100.0) was achieved below 20 ppb (165% predicted). FeNO is a sensitive and specific tool for predicting the response to inhaled mannitol in an unselected sample of non-smoking, steroid-naïve subjects, and a low FeNO indicates that extra diagnostic work-up using inhaled mannitol will add very little extra information.