OBJECTIVE: To confirm the relevance of upper and lower airway inflammation in eosinophilic chronic rhinosinusitis (ECRS), the effects of endoscopic sinus surgery (ESS) on lower airway functions and inflammation need to be examined in ECRS patients. METHODS: Chronic rhinosinusitis patients with nasal polyps (25 non-ECRS, 28 ECRS) were enrolled. The 12 patients in the ECRS group had comorbid asthma, in contrast to none in the non-ECRS group. We divided ECRS patients into 2 groups of ECRS with and without asthma. Clinical markers, including fraction of exhaled nitric oxide (FeNO), respiratory functions, and the Asthma Control Test (ACT) questionnaire, were investigated before and after ESS. RESULTS: The FeNO levels in the ECRS with asthma group decreased after ESS. The mean FeNO levels in this group were 56.3 ppb before ESS and 24.9, 25.1, 25.0, and 15.5 ppb 1, 2, 3, and 4 months, respectively, after ESS. The mean forced expiratory rates in 1 second before and after ESS were 67.6% and 73.0%, respectively. The mean maximal expiratory flow rates at 50% of the vital capacity before and after ESS were 45.8% and 58.0%, respectively. Significant differences were observed in respiratory functions before and after ESS. The mean ACT scores in the ECRS with asthma group before and after ESS were 17.5 and 23.5, respectively. The ACT scores were significantly higher after than before ESS. CONCLUSIONS: The present results indicate that ECRS and bronchial asthma are common eosinophilic airway inflammatory diseases, and ESS for eosinophilic sinusitis may improve lower airway function.