Background: Patients with dementia commonly suffer from symptoms of overactive bladder (OAB); however, limited research exists on the clinical impact of coexisting OAB among patients with dementia. As such, the objective of this study was to examine the impact of OAB on clinical outcomes, health-care resource use, and associated costs among patients with dementia. Methods: We conducted a retrospective cohort analysis of patients with dementia using 3861 matched pairs of patients with and without OAB. Analyses were based on administrative claims data from January 1, 2007, to September 30, 2015, and compared clinical outcomes, health services use, and associated costs. Results: Patients with dementia and OAB were more likely than those without OAB to have least one fall (incidence rate ratio [IRR]: 1.43, 95% confidence interval [CI], 1.22-1.68, P < .001), fracture (IRR: 1.23, 95% CI, 1.05-1.44, P = .008), combined fall/fracture (IRR: 1.25, 95% CI, 1.11-1.42, P < .001), or urinary tract infection (IRR: 2.75, 95% CI, 2.55-2.96, P < .001). Patients with dementia and OAB demonstrated greater utilization of all-cause encounter types compared to similar patients without coexisting OAB ( P < .01). All-cause and dementia-related total health-care costs were approximately 23% (95% CI, 0.19-0.28, P < .001) and 13% (95% CI, 0.05-0.20, P = .001), respectively, greater than similar patients without coexisting OAB. Conclusion: Coexisting OAB was associated with impacts on clinical outcomes, health-care resource utilization, and costs in patients with dementia.