Studies show a strong association between dementia and lower urinary tract symptoms (LUTS). The aim of this study was to investigate whether LUTS are a risk factor for cognitive impairment. We enrolled 50-year-old and older subjects with LUTS (LUTS([+])) (n = 6801) and controls without LUTS (LUTS([-])) (n = 20,403) from Taiwan's National Health Insurance Research Database. LUTS, dementia, and other confounding factors are defined by International Classification of Diseases, Ninth Revision, Clinical Modification Codes. Participants were recruited from 2000 to 2004 and then followed up until death or the end of 2011. The outcome was the onset of dementia, which was assessed using Poisson regression analysis, Cox hazards models, and Kaplan-Meier survival curves. The incidence of dementia was significantly higher in the LUTS([+]) group than in the LUTS([-]) group (124.76 versus 77.59/1000 person-years). The increased risk of dementia related to LUTS remained significant after adjustment for potential confounders (adjusted hazard ratio (AHR): 1.61, 95% confidence interval (CI) 1.47-1.76, P < 0.0001) and higher than that related to cerebrovascular disease (AHR: 1.43, 95% CI 1.26-1.61, P < 0.0001). The outcome suggests the need for early screening and appropriate intervention to help prevent cognitive impairment of patients with LUTS.