Inhaled anticholinergic medications are widely used treatments for chronic obstructive pulmonary disease (COPD); however, their systemic effects have not been widely studied. Using linked administrative health care data from Ontario, Canada, this population-based nested case-control study sought to determine the risk of acute urinary retention (AUR) in seniors with COPD prescribed inhaled anticholinergic medications. Of 565 073 individuals with COPD, Stephenson et al identified 11 238 cases of AUR. Compared with matched controls, men who were new users of inhaled anticholinergic therapy had a more than 40% greater odds of developing AUR compared with nonusers after adjusting for multiple covariates. This risk increased further in men with benign prostatic hyperplasia (odds ratio, 1.81; 95% confidence interval, 1.46-2.24). When prescribed both a short- and long-acting inhaled anticholinergic medication, men had a significantly higher risk of AUR compared with nonusers (odds ratio, 2.69; 95% confidence interval, 1.93-3.76). The risk of AUR in women was not statistically significant.