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This study was undertaken to a) evaluate whether exhaled nitric oxide (fraction of exhaled nitric oxide [Feno]) levels are reflective of asthma severity in concordance with the National Asthma Education and Prevention Program categorization and b) determine the usefulness of Feno using the single-breath exhalation technique for monitoring asthma control and compliance with steroid treatment.Thirty patients with asthma (7–17 yrs old; 14 males and 16 females) that was mild (n = 8), moderate (n = 17), or severe (n = 5) were included in the study. Fifteen patients were seen on more than one occasion for a total of 53 visits. Information obtained at each visit included asthma symptoms, β-agonists and corticosteroids use, compliance to steroids, and forced expiratory volume in 1 sec (Fev1) and Feno measurements. Asthma control was judged by a pulmonologist based on overall evaluation of symptoms, Fev1 measurements, and the frequency of β-agonists use at each visit.The mean ± sd Feno was significantly different in the mild, moderate, and severe asthma categories (30 ± 12, 65 ± 48, 104 ± 68, respectively; F2,52 = 6.02 p = .005). Feno was significantly correlated with asthma severity (r = .44, p = .001), compliance (r = −.75, p = .001), and control (r = −.51, p = .001). There were no statistically significant differences between asthma severity and compliance or Fev1.Our data suggest that a) Feno may be a practical tool to evaluate asthma severity and asthma control over time and b) Feno may be used as a marker of compliance with steroids even when Fev1 has not decreased significantly.