The associations between blood pressure and dementia have been inconclusive. We followed up a total of 668 community-dwelling Japanese individuals without dementia, aged 65 to 79 years, for 17 years and examined the associations of late-life and midlife hypertension with the risk of vascular dementia and Alzheimer disease using the Cox proportional hazards model. During the follow-up, 76 subjects experienced vascular dementia and 123 developed Alzheimer disease. The age- and sex-adjusted incidence of vascular dementia significantly increased with elevated late-life blood pressure levels (normal: 2.3, prehypertension: 8.4, stage 1 hypertension: 12.6, and stage 2 hypertension: 18.9 per 1000 person-years; P_trend<0.001), whereas no such association was observed for Alzheimer disease (P_trend=0.88). After adjusting for potential confounding factors, subjects with prehypertension and stage 1 or stage 2 hypertension had 3.0-fold, 4.5-fold, and 5.6-fold greater risk of vascular dementia, respectively, compared with subjects with normal blood pressure. Likewise, there was a positive association of midlife blood pressure levels with the risk of vascular dementia but not with the risk of Alzheimer disease. Compared with those without hypertension in both midlife and late life, subjects with midlife hypertension had an ≈5-fold greater risk of vascular dementia, regardless of late-life blood pressure levels. Our findings suggest that midlife hypertension and late-life hypertension are significant risk factors for the late-life onset of vascular dementia but not for that of Alzheimer disease in a general Japanese population. Midlife hypertension is especially strongly associated with a greater risk of vascular dementia, regardless of late-life blood pressure levels.