Background Use of inhaled corticosteroids (ICS) is common in patients with chronic obstructive pulmonary disease (COPD) and has been associated with an increased risk of pneumonia. Moraxella catarrhalis is one of the most common bacterial causes of infectious exacerbation in COPD. Currently, to our knowledge, no studies have investigated if ICS increases the risk of lower respiratory tract infection with M. catarrhalis in patients with COPD. Objective To investigate if accumulated ICS use in patients with COPD, is associated with a dose-dependent risk of infection with M. catarrhalis. Methods This observational cohort study included 18 870 persons with COPD who were registered in The Danish Register of COPD. Linkage to several nationwide registries was performed. Exposure to ICS was determined by identifying all prescriptions for ICS, redeemed within 365 days prior to study entry. Main outcome was a lower respiratory tract sample positive for M. catarrhalis. For the main analysis, a Cox multivariate regression model was used. We defined clinical infection as admission to hospital and/or a redeemed prescription for a relevant antibiotic, within 7 days prior to 14 days after the sample was obtained. Results We found an increased, dose-dependent, risk of a lower respiratory tract sample with M. catarrhalis among patients who used ICS, compared with non-users. For low and moderate doses of ICS HR was 1.65 (95% CI 1.19 to 2.30, p=0.003) and 1.82 (95% CI 1.32 to 2.51, p=0.0002), respectively. In the group of patients with highest ICS exposure, the HR of M. catarrhalis was 2.80 (95% CI 2.06 to 3.82, p<0.0001). Results remained stable in sensitivity analyses. 87% of patients fulfilled the criteria for clinical infection, and results remained unchanged in this population. Conclusion Our study shows a dose-dependent increased risk of infection with M. catarrhalis associated to ICS exposure.