BACKGROUND: Many studies have examined differences in hypertension across race/ethnic groups but few have evaluated differences within groups. METHODS: We investigated within-group geographic variations in hypertension prevalence among 3,322 black and white participants of the Multi-Ethnic Study of Atherosclerosis (MESA). Place of birth and place of residence were included in multivariate Poisson regression analyses. RESULTS: Blacks born in southern states were 1.11 (95% confidence interval (CI): 1.02, 1.23) times more likely to be hypertensive than non-southern states after adjusting for age and sex. Findings were similar, though not statistically significant, for whites (prevalence ratio (PR): 1.15, 95% CI: 0.98, 1.35). Blacks and whites living in Forsyth (blacks, PR: 1.23, 95% CI: 1.07, 1.42; whites, PR: 1.32, 95% CI: 1.09, 1.60) and Baltimore (blacks, PR: 1.14, 95% CI: 1.00, 1.31; whites, PR: 1.24, 95% CI: 1.05, 1.47) were also significantly more likely to be hypertensive than those living in Chicago after adjusting for age and sex. Among blacks, those living in New York were also significantly more likely to be hypertensive. Geographic heterogeneity was partially explained by socioeconomic indicators, neighborhood characteristics or hypertension risk factors. There was also evidence of substantial heterogeneity in black-white differences depending on which geographic groups were compared (ranging from 82 to 13% higher prevalence in blacks compared with whites).http://deepblue.lib.umich.edu/bitstream/2027.42/78514/1/KershawDiezRoux2010_AmJHTN.pdf