Objective To determine if the therapeutic response to an inhaled corticosteroid is attenuated in individuals with asthma who smoke.Methods 38 outpatients with chronic stable asthma who visited during March 2008 and January 2009 were enrolled in the study. 23 cases were nonsmokers and 15 cases were smokers. All of them were treated by daily inhaled budesonide, and β2 agonist when necessary.They were required to record symptoms and peak expiratory flow every day on an asthmatic diary card. Thepatients were followed 28 days. ACT score, asthma-symptom score, Asthma Control Test ( ACT) score,pulmonary function, and peak expiratory flow were compared between the non-smoking and the smoking asthmatic patients. Results All of the patients had statistically significant increases in ACT score, mean morning and night PEF, mean forced expiratory volume in 1 second, and a significant decrease in asthmasymptom score after budesonide treatment compared with before. There were significantly greater changes inany of these parameters in the non-smokers than in the smokers. Conclusions Active cigarette smoking impairs the efficacy of short term inhaled corticosteroid treatment in asthma. This finding has important implications for the management of patients with asthma who smoke.