Background: Nasal nitrous oxide (nNO) is increased in allergic rhinitis (AR), but not in asthma, and is a non-invasive marker for inflammation in the nasal passages. Methods: Levels of nNO were measured and compared in healthy children and children with mild and moderateto-severe AR. Levels of nNO before and after treatment with steroids and/or antihistamine were then compared in the 2 AR groups. Their relationship to quality of life and nasal symptom and reactivity to outdoor and outdoor allergens were examined. Results: nNO levels were higher in mild AR than in healthy children and higher in moderate-to-severe AR than in mild AR. One month steroid and/or antihistamine treatment lowered nNO levels to control levels in mild AR and approximately halfway to control levels in moderate-to-severe AR. nNO levels had a weak correlation to quality of life questions and a fair correlation to nasal symptom scores before treatment. This correlation was weakened or lost after treatment, and no correlation was seen between nNO levels and responses to indoor or outdoor allergens. Conclusion: nNO levels in children with AR may be useful for assessing the response to treatment. Their relationship to quality of life, nasal symptoms, and sensitivity to specific allergens needs further study.