BACKGROUND: Obesity is a risk factor for chronic venous insufficiency and venous thromboembolism. The aim of this study was to compare venous flow parameters of the lower limbs assessed by duplex ultrasound scanning in obese and nonobese individuals according to body mass index (BMI). METHODS: Venous hemodynamics were studied in a prospective cohort study in nonobese (BMI <25 kg/m(2)) and obese individuals (BMI >30 kg/m(2)). Diameter, flow volume, peak, mean, and minimum velocities were assessed. RESULTS: The study examined 36 limbs in 23 nonobese individuals and 44 limbs in 22 obese individuals. The diameter of the femoral vein was significantly greater in obese (8.5 +/- 2.2 mm) vs nonobese (7.1 +/- 1.6 mm; P = .0009) limbs. Venous peak and minimum velocities differed between nonobese and obese individuals (14.8 +/- 7.2 vs 10.8 +/- 4.8 cm/s [P = .0071] and 4.0 +/- 3.6 vs 1.7 +/- 6.3 cm/s [P = .056]). Calculation of venous amplitude and shear stress showed significantly higher values in nonobese vs obese (18.8 +/- 9.4 vs 12.5 +/- 9.3 cm/s [P = .003] and 2.13 +/- 2.2 dyn/cm(2) vs 1.6 +/- 2.7 dyn/cm(2) [P = .03]). Spearman rank correlation revealed a significant inverse correlation between waist-to-hip ratios and waist circumference and venous peak velocity, mean velocity, velocities amplitude (peak velocity-minimum velocity), and shear stress. CONCLUSION: Lower limb venous flow parameters differ significantly between healthy obese and nonobese individuals. These findings support the mechanical role of abdominal adipose tissue potentially leading to elevated risk for both venous thromboembolism and chronic venous insufficiency.