ABSTRACT Background Numerous studies have linked dementia to the subsequent deterioration of oral health. Few investigators, however, have examined oral disease as a potential risk factor in the development of dementia. The authors conducted a study to investigate a potential association between a history of oral disease and the development of dementia. Methods Longitudinal dental records supplemented data collected from 10 annual cognitive assessments of 144 Milwaukee participants in the Nun Study, a longitudinal study of aging and Alzheimer disease, who were 75 to 98 years old. Neuropathologic findings at autopsy were available for 118 participants who died. Results A low number of teeth increased the risk of higher prevalence and incidence of dementia. Conclusion Participants with the fewest teeth had the highest risk of prevalence and incidence of dementia. Clinical Implications Edentulism or very few (one to nine) teeth may be predictors of dementia late in life.