The survey of early-onset dementia was done in fve prefectures and two cities in all parts of Japan from 2006 to 2008. The estimated number of patients per 100,000 in the 18–64-year-old population was 47.6 (95% confdence interval (CI): 45.5–49.7). The estimated patient number in all of Japan was calculated to be 37,800 (95% CI: 36,100–39,400). As a result, we found that vascular dementia (VaD) was the most common illness causing dementia, followed by Alzheimer’s disease (AD), posttraumatic syndrome, and then frontotemporal degeneration. The prevalence of late-onset dementia was surveyed with in ten areas in all parts of Japan from 2009 to 2012. From the results, the estimated national prevalence was 15%, with a standard error of 0.0136 and 95% CI of 0.12, 0.17. The number of people with dementia in all of Japan was estimated to be about 4.62 million out of a population of 30.79 million people (defnite value) aged 65 years and older as of October 1, 2012. The number had probably reached 50 million by the end of 2014. For the immediate future, both the prevalence and the total number of dementia patients are expected to rise steadily with the increase in the mean life expectancy.