The ankle-brachial blood pressure index (ABI) is a widely utilized measure for detecting peripheral arterial disease. Genetic contributions to variation in ABI are largely unknown. The authors sought to estimate ABI heritability in a community-based sample. From 1995 to 1998, ABI was measured in 1,097 men and 1,189 women (mean age = 57 years; range, 29-85 years) from 999 families in the Framingham Offspring cohort. Correlation coefficients for sibling pairs were calculated using the family correlations (FCOR) procedure in S.A.G.E. (Case Western Reserve University, Cleveland, Ohio). The heritability of ABI was estimated using variance-components methods in SOLAR (Southwest Foundation for Biomedical Research, San Antonio, Texas). Analyses were performed on normalized crude ABI and on normalized residuals from multiple linear regression analyses in SAS (SAS Institute, Inc., Cary, North Carolina) that adjusted for age, sex, smoking, diabetes, hypertension, ratio of total cholesterol to high density lipoprotein cholesterol, log triglyceride level, and body mass index. The mean ABI was 1.1 (range, 0.4-1.4). The age- and sex-adjusted and multivariable-adjusted sibling-pair correlation coefficients for normalized ABI were 0.15 and 0.11, respectively, resulting in heritability estimates of 0.30 and 0.22. Crude, age- and sex-adjusted, and multivariable-adjusted heritabilities for normalized ABI estimated using variance-components analysis were 0.27 (standard error, 0.06), 0.30 (standard error, 0.06), and 0.21 (standard error, 0.06), respectively (all p values < 0.0001). A modest proportion of the variability in ABI is explained by genetic factors.