Cognitive impairment leading to dementia is associated with high prevalence of hypertension, decreased quality of life and poor prognosis. Aldosterone is known as a risk factor for cardiovascular and cerebrovascular diseases. In addition, mineral corticoid receptors are abundantly expressed in the hippocampus, which plays a pivotal role in cognitive function; however, it has not been determined whether plasma aldosterone level is associated with cognitive impairment in patients with hypertension. We enrolled 68 patients with essential hypertension and assessed their cardiovascular risk factors, including blood pressure, hyperlipidemia, diabetes mellitus, obesity, smoking, history of cerebral infarction, renal function, parameters of inflammation, oxidative stress and nitric oxide bioavailability, a parameter of cerebral blood flow and carotid plaque by ultrasound examination, plasma renin activity and plasma aldosterone concentration (PAC). The mini-mental state examination (MMSE) was used to evaluate cognitive function. The relevance of cardiovascular risk factors and MMSE score was statistically evaluated. Multiple regression analysis showed that age (P < 0.01), PAC (P < 0.01) and history of cerebral infarction (P < 0.05) were inversely and independently associated with MMSE score. Mineral corticoid receptor antagonists, including spironolactone and eplerenone, increased MMSE score in seven patients with hypertension, but not in the controls. In conclusion, increased PAC is associated with impaired cognitive function and mineral corticoid receptor blockade may protect against not only cardiovascular mortality, but also cognitive impairment in patients with hypertension.