In dementia with Lewy bodies (DLB), the Lewy bodies (LBs) are an essential substrate. Although LB pathology has gained increasing attention as one of the major causes of dementia, little is known about the exact prevalence of LB pathology in the general population. In addition, the pathology of Alzheimer-type dementia (ATD) is frequently associated with DLB. To investigate the prevalence of LB pathology in a community-based population and to evaluate the relationship between LB and ATD pathology, we performed an analysis of 102 consecutive autopsy cases. The survey extended over 2.5 years and autopsy rate was 70.5%. LB pathology was detected using alpha-synuclein immunohistochemistry and was assessed based on consensus guidelines for DLB. ATD pathology was evaluated by both CERAD and NIA-RI criteria. Twenty-nine subjects were clinically demented. LB pathology was present in 23 (22.5%) of 102 cases, and in 12 (41.4%) of the demented subjects. The LB score was not significantly different between DLB cases and non-demented subjects with LB pathology (nd-LB), while the Braak stages were significantly different between the two groups. Prevalence of LB pathology constantly increased with age. DLB cases accompanying severe ATD pathology showed more rapid increase of LB scores than did DLB cases without severe ATD pathology. Moreover, DLB cases with severe ATD pathology had poorer prognoses than those without severe ATD pathology. Our results suggested that aging and severe ATD pathology have a strong effect on the evolution of LB pathology.