OBJECTIVE: To evaluate the relationship between blood pressure (BP) and cognitive impairment in elderly populations in India and the United States in a cross-national epidemiological study. DESIGN: Cross-sectional comparisons, using standardized cognitive screening and BP measurements. PARTICIPANTS: We examined 4810 subjects 55 years and older, of whom 595 were 75 years and older, from Ballabgarh, India, and 636 subjects 75 years and older from the Monongahela Valley, Pennsylvania. MAIN OUTCOME MEASURES: General cognitive impairment, defined as scores at or below the 10th percentile of each cohort on a general mental status test-the Mini-Mental State Examination (United States) and the Hindi Mental State Examination (India)-and memory impairment, defined as scores at or below the 10th percentile of delayed recall of word lists at both sites. RESULTS: Mean systolic BP (SBP) and diastolic BP (DBP) were 115 and 75 mm Hg (India) and 141 and 76 mm Hg (United States). Logistic regression adjusting for age, sex, and education or literacy was used to calculate odds ratios (ORs) and associated 95% confidence intervals (CIs) for cognitive impairment. In Ballabgarh, for every 10 mm Hg increase in SBP there was a 10% reduction in cognitive impairment (OR, 0.90; 95% CI, 0.83-0.97), and there was a 13% reduction in cognitive impairment (OR, 0.87; 95% CI, 0.76-0.99) with every 10 mm Hg increase in DBP. In the Monongahela Valley, a similar association between DBP and cognitive impairment did not remain significant after adjustment for confounders (OR, 0.83; 95% CI, 0.65-1.06). CONCLUSIONS: In both Indian and American samples, lower DBP was inversely related to cognitive impairment, although not significantly in the latter. Low BP may be an effect of, or a potential risk factor for, degenerative brain disease.