Epidemiologic studies investigating the differences in respiratory outcomes between asthma-chronic obstructive pulmonary disease overlap syndrome (ACOS) and chronic obstructive pulmonary disease (COPD) in an Asian population are lacking.We conducted a population-based cohort study to compare the incidence of acute respiratory events between ACOS and COPD cohorts in Taiwan. This study investigated the incidence of acute respiratory events, namely, pneumonia, acute exacerbation, acute respiratory failure, and cardiopulmonary arrest, in 8571 patients with physician-diagnosed ACOS between 2000 and 2007 from the Longitudinal Health Insurance Database. The comparison cohort comprised 17,088 COPD patients, frequency-matched according to age, sex, and the index-year. The duration of follow-up was measured for each patient from the index date to 5 years thereafter. We used univariable and multivariable Poisson regression models to analyze the risk of acute respiratory events by including the variables of sex, age, and comorbidity.The overall prevalence of ACOS was approximately 17.4% in patients with COPD. The prevalence of ACOS increased with age. During the 5-year follow-up, a greater incidence of acute respiratory events was observed in the ACOS cohort than in the COPD cohort (11.5 and 4.62, per 100 person-years, respectively) with an adjusted incidence rate ratio (IRR) of 1.72 (95% confidence interval [CI] = 1.63-1.81). Compared with the COPD cohort, the ACOS patients had a 1.13-fold adjusted IRR of pneumonia (95% CI = 1.07-1.20) and a 2.58-fold adjusted IRR of acute exacerbation (95% CI = 2.43-2.74). Clinicians should be aware of frequent exacerbation of ACOS and prescribe appropriate treatment.