The goal of the present study was to evaluate mean values and heritability estimates of 3 global and 11 regional obesity measures in siblings with (HPT, n=209) or without (non-HPT, n=91) early-onset (age </=55 years) hypertension who originated from the same families. Sixty-one sibships, each having at least 2 HPT siblings, were selected from a French-Canadian population with a known founder effect. Comparison of the mean values showed that HPT siblings are more obese than non-HPT siblings and that the body fat of HPT siblings is more centrally distributed. Significant differences were observed in all global obesity measures (P=0.009 to 0.0001). Among the regional measures, the most prominent differences were seen in waist circumference (P=0.00002), waist/hip ratio (P=0.0001), and suprailiac skinfold (P=0.00008). Comparison of the heritability estimates derived from sibling/sibling correlations (FCOR program, SAGE) suggested that genetic factors play a greater role in HPT (n=357) than in non-HPT (n=93) sib-pairs in determining most obesity measures. Similar to the mean values, these differences were most apparent in global and upper-body measures, with heritabilities ranging from 40% to 70% (P=0.05 to 0.0006) in HPT siblings and from 0% to 32% (P=NS) in non-HPT siblings. In summary, the present results suggest that HPT and non-HPT siblings drawn from the same families differ by the degree and distribution of body fat accumulation and that this difference is determined, at least in part, by genetic factors cosegregating with hypertension. This, in turn, suggests that a genetic link exists between obesity and hypertension in these families.