OBJECTIVE: This study aims to synthesise evidence on time trends of dementia prevalence in East Asian countries including Japan, China, South Korea and Taiwan and assess the impact of the societal changes on future prevalence. METHOD: Relevant reviews and recent nationwide studies in East Asia were identified to investigate changes in prevalence of dementia over time taking into account the potential impact of methodological factors and study designs. RESULTS: The robust evidence that has been interpreted to suggest a substantial increasing trend over time is less compelling once fundamental differences in study methods and populations across individual surveys are considered. In Japan, longitudinal studies in small areas suggest the potential increase of prevalence after 2000. Increasing trends in China, South Korea and Taiwan over the last 20-30 years are based on the literature review without adjustment for methodological differences. Economic development and huge societal changes alongside the rise of non-communicable disease in East Asia could lead to increasing prevalence of dementia in the future once those cohorts with high risk of dementia reached their older age. CONCLUSION: Current evidence is not sufficient to suggest increasing trends of dementia prevalence in East Asia. Longitudinal studies with representative samples and stable methodology are needed to provide fundamental information of the epidemiology of dementia and identify important risk factors in East Asian societies.