The aim of the present study was to examine the prevalence and causes of adult epilepsy in a general Japanese population. We examined a total of 3333 Japanese residents in the town of Hisayama aged ≥40 years in 2012-2013. The examination was performed mainly at the municipal center for health promotion, but some subjects were examined in their homes, hospitals, or nursing homes. Twenty-three subjects had a diagnosis of epilepsy. The prevalence (95% confidence interval [CI]) of epilepsy per 1000 was 6.9 (4.1-9.7) in total, 4.9 (1.3-8.5) in men, and 8.4 (4.3-12.5) in women (=0.23 between sexes). The prevalence of epilepsy was significantly higher in the elderly (aged ≥65 years; 10.3 per 1000 [95% CI 5.4-15.1]) than in the middle-aged (aged 40-64 years; 3.6 per 1000 [95% CI 0.7-6.4]; =0.02). The major cause of epilepsy was cerebrovascular diseases (n = 11; 48% of the epilepsy patients). More than half of the epilepsy patients experienced the first episode of seizure in older age (≥65 years; n = 13; 57%). The findings of this study suggest the clinical importance of the prevention of cerebrovascular diseases to reduce the burden of epilepsy in the future.