Background: While asthma control is defined as the extent to which the various manifestations of asthma are reduced by treatment, current guidelines of asthma recommend assessment of asthma control without consideration of airway inflammation. Our aim was to investigate the relationships between fractional exhaled nitric oxide (FeNO), a reliable marker of airway inflammation, and levels of asthma control in patients treated with inhaled corticosteroids (ICS). Methods: We enrolled 71 adult patients with asthma who had been treated with ICS for more than four months. FeNO was measured and spirometry was performed at the time of enrollment. Asthma control was assessed (a) by the physician based on the Global Initiative for Asthma guidelines, (b) by the patients, and (c) by using the Asthma Control Test (ACT). Statistical analyses were done to analyze the relationships between (i) FeNO and (ii) measures of asthma control and clinical indices for asthma manifestations. Results: There was no significant difference in FeNO levels between the three groups according to levels of asthma control (controlled, partly controlled and uncontrolled) as determined by the physician (p=0.81), or by the patients (p=0.81). In addition, FeNO values were not significantly correlated with the ACT scores (r=0.031, p=0.807), while FeNO showed a correlation with peripheral blood eosinophil counts (p<0.001). Conclusion: These findings demonstrate that FeNO levels are not associated with measures of asthma control in patients treated with ICS. Information on airway inflammation from FeNO concentrations seems to be unrelated to levels of asthma control