We examined long-term changes in cognitive function and quality of life (QL) in hypertensive patients by comparing the antihypertensive effect of hydrochlorothiazide (HCTZ) and losartan. We studied 69 patients (age range, 30 to 73 years) with mild-to-moderate hypertension. All patients, in a double-blind study, were randomly allocated to either treatment with 50 mg losartan once daily or 25 mg HCTZ once daily. The sample in each treatment group was divided by age (younger than 60 years or 60 years or older). At baseline and after 26 months, a QL questionnaire appropriate for the hypertensive patients was given. Cognitive function was evaluated, at baseline and after 26 months, by psychometric tests consisting of items from the Mini-Mental State Examination (MMSE) and the Sandoz Clinical Assessment Geriatric (SCAG). A score of less than 24 on the MMSE and more than 40 on the SCAG was predictive of cognitive impairment. The losartan group had a significant improvement in SCAG (P<.001) and MMSE (P<.001). No significant changes were observed in the HCTZ group (SCAG, P = .1; MMSE, P = .2). Sixty-five percent of the elderly had a MMSE score less than 24 and 70% had a SCAG score greater than 40, v. 35% and 48%, respectively, in younger patients. The health state index of QL improved significantly in both groups (losartan group, P<.01; HCTZ group, P<.02); the improvement in QL scores in patients using HCTZ was significant only in subjects aged 60 years and older (P<.04). These results suggest that losartan can have a positive effect not only on blood pressure but also on impaired cognitive function, reversing even minimal cognitive deficits induced by hypertension. The elderly patients in our sample had worse scores and cognitive performance was lower than in younger patients, even if in the losartan group the score improvement was the same at all ages. The same could not be said for HCTZ.