['Inhaled corticosteroid (ICS) is recommended in the management of patients with asthma-chronic obstructive pulmonary disease overlap syndrome (ACOS), but its effectiveness has not been clearly proved.', 'To evaluate whether ICS has effects on outcomes of ACOS.', 'In this observational 12-year retrospective cohort study involving 125 patients with ACOS from Seoul National University Hospital, the annual rate of decrease in forced expiration volume in 1 second, the incidence rate of severe exacerbation, and overall mortality in an ICS-treated group were compared with those in a non-ICS-treated group.', 'Of 125 patients with ACOS, 90 and 35 were categorized to the ICS and non-ICS treatment groups, respectively. There were no significant differences between the 2 groups in the annual rate of decrease in forced expiration volume in 1 second (9.61 mL/year in ICS treatment group vs 15.68 mL/year in non-ICS treatment group, P\xa0= .598). Compared with the non-ICS treatment group, the ICS treatment group did not show a decrease in the risk of severe exacerbation (adjusted incidence rate ratio 1.24, 95% confidence interval 0.44-3.46). Time to death also did not differ between the 2 groups. Even when analyses with propensity score matching were performed, the results were similar.'] Do responsiveness to inhaled corticosteroid treatment in patients with asthma-chronic obstructive pulmonary disease overlap syndrome?