Arterial hypertension in midlife may increase the risk of late-life dementia. Notably, there is conflicting data as to whether hypertension in the elderly (age 65 years and older) is a risk factor for dementia and Alzheimer's disease (AD). We determined whether drug-untreated hypertension was associated with a higher risk of incident dementia and AD. In a population-based study of older people in central Spain (NEDICES), non-demented participants were followed prospectively. Dementia at follow-up was diagnosed using DSM-IV criteria. Using Cox proportional hazards models, the risk of dementia was estimated in participants with drug-untreated hypertension and in participants with drug-treated hypertension versus controls. The 3,824 participants had a mean duration of follow-up of 3.2 years. Sixty-two (3.3%) of 1,870 participants without baseline hypertension developed incident dementia versus 78 (4.7%) of 1,657 with drug-treated, baseline hypertension and 19 (12.0%) with drug-untreated, baseline hypertension. In an unadjusted Cox model, risk of dementia was increased in participants with drug-untreated hypertension (relative risk [RR] =1.93, 95% confidence interval [CI]=1.15–3.23, p = 0.01) and in participants with drug-treated hypertension (RR =1.43, 95% CI= 1.02–2.0, p =0.035) versus participants without hypertension (reference group). In a fully adjusted Cox model, the risk of dementia remained increased in participants with drug-untreated hypertension (RR =2.38, 95% CI =1.32–4.29, p=0.004). Results were similar for risk of AD. Our results suggest that drug-untreated hypertension may be an independent risk factor for dementia and AD in the elderly.