We investigated the effect of the long-acting muscarinic antagonist aclidinium bromide on chronic obstructive pulmonary disease (COPD) exacerbations by pooling data from five randomized, placebo-controlled,parallel-group Phase III studies of 3-6 months' duration. Data were pooled from the aclidinium 400 μg twice-daily (BID) and placebo arms (N = 2,521) and stratified by Global initiative for chronic Obstructive Lung Disease (GOLD) group (A, B, C and D). Results showed that fewer patients experienced 1 exacerbation with aclidinium (any severity: 12.5%; moderate to severe: 10.9%) compared with placebo (any severity: 15.7%; moderate to severe: 13.3%) and the odds of experiencing 1 exacerbation of any severity were reduced in patients receiving aclidinium (odds ratio = 0.78, p = 0.039). Furthermore, aclidinium reduced the rate of exacerbations compared with placebo (any severity: rate ratio = 0.79, p = 0.026; moderate to severe: 0.80, p = 0.044). The time to first exacerbation of any severity was delayed with aclidinium compared with placebo (hazard ratio = 0.79, p = 0.026) and there was a numerical delay in time to first moderate-to-severe exacerbation. Finally, the effects of aclidinium on exacerbations versus placebo were greater in patients in GOLD Groups B and D; however, it is of note that only 10.7% of patients were classified in Group A or C. In summary, the results indicate that aclidinium 400 μg BID reduces the frequency of COPD exacerbations compared with placebo and that these effects are greater in symptomatic patients.