Summary As an ‘inflammometer’, the fraction of nitric oxide in exhaled air (FeNO) is increasingly used in the management of paediatric asthma. FeNO provides us with valuable, additional information regarding the nature of underlying airway inflammation, and complements lung function testing and measurement of airway hyper‐reactivity. This review focuses on clinical applications of FeNO in paediatric asthma. First, FeNO provides us with a practical tool to aid in the diagnosis of asthma and distinguish patients who will benefit from inhaled corticosteroids from those who will not. Second, FeNO is helpful in predicting exacerbations, and predicting successful steroid reduction or withdrawal. In atopic asthmatic children FeNO is beneficial in adjusting steroid doses, discerning those patients who require additional therapy from those whose medication dose could feasibly be reduced. In pre‐school children FeNO may be of help in the differential diagnosis of respiratory symptoms, and may potentially allow for better targeting and monitoring of anti‐inflammatory treatment.