목적: Chronic eosinophilic pneumonia (CEP) is a disorder characterized by chronic or recurrent eosinophilic infiltration of the lung. It is dramatically responsive to corticosteroid therapy, but relapses are frequent after tapering or stopping the corticosteroid. The fraction of exhaled nitric oxide (FeNO) is a well-known marker of eosinophilic inflammation of the lung. The aim of this study was to evaluate the correlation between FeNO and serum eosinophil levels in CEP patients during follow-up. 방법: We retrospectively reviewed the clinical information and FeNO levels in CEP patients treated at Seoul National University Bundang Hospital from June 2004 to June 2012. We measured FeNO and serum eosinophil levels, and took a chest radiograph at every outpatient visit. 성적: Eighteen patients were enrolled during this period (10 males; median age, 58 years). Thirteen (72.2%) patients had never been smokers. A history of asthma was present in eight (44.4%) of the patients. A combined total of 50 FeNO measurements were available for the patients. Based on Pearson`s correlation, FeNO was positively correlated with peripheral blood eosinophil count (r=0.31, p=0.034) and eosinophil percentage (r=0.37, p=0.011). Three patients had acute exacerbation of their CEP, and their increased FeNO levels were improved with steroid therapy. 결론: In patients with CEP, FeNO is correlated with serum eosinophils and may be a useful parameter in evaluating treatment effectiveness and determining appropriate medication adjustments.