To estimate common and distinct genetic influences on a panel of obesity-related traits and serum leptin level in adults. In a cross-sectional study of 625 Danish, adult, healthy, monozygotic, and same-sex dizygotic twin pairs of both genders, we carried out detailed anthropometry (height, weight, waist and hip, and skin-fold thickness, body composition assessment by bioimpedance (fat mass and fat-free mass), and measurement of serum leptin level. Bivariate variance component analyses estimated the additive genetic correlations between these measurements. The genetic correlations between the traits for overall fatness (BMI and fat mass index, kg/m(2)) were 0.94 in men and 0.98 in women, and their correlations with the various local fatness measures ranged from 0.49 to 0.83 in men and from 0.70 to 0.87 in women. The correlations between the truncal measures (waist circumference and truncal skin folds) and between the peripheral measures (hip circumference and peripheral skin folds) were 0.57 and 0.47 in men and 0.71 and 0.70 in women, respectively. The correlations between the truncal and peripheral measures ranged between 0.49 and 0.72 in men and between 0.61 and 0.82 in women. For leptin vs. the various measures of overall and local fatness the correlations ranged from 0.54 to 0.74 in men and from 0.48 to 0.75 in women. All correlations were significantly <1.00. The study supports control of overall fat mass and peripheral and truncal fat mass by both shared and different genetic components, which suggests that it is important to distinguish between the different phenotypes in the search for genes involved in the development of obesity.