Obesity in childhood has been associated with the development of early cardiovascular abnormalities. The aim of the present study was to investigate whether preclinical functional changes are detectable in the abdominal aorta of obese children. One hundred consecutively seen obese children and 50 healthy controls were studied. The groups were matched in terms of age and gender. The pulsatile wall-motion of the abdominal aorta was determined using a B-mode ultrasound technique. The following mechanical property parameters were measured or computed: lumen diastolic and systolic diameters, relative aortic strain, elastic modulus, and stiffness. Compared to controls, obese children had higher blood pressure values and higher concentrations of total cholesterol, triglycerides, insulin, and C-reactive protein. Homeostasis model assessment (HOMA) score, a parameter of insulin resistance, was significantly higher in obese children than in controls (3.2 +/- 1.9 v 1.4 +/- 0.5, P <.001). Aortic mechanical parameters were significantly different in obese children as compared to controls: stiffness was higher (3.00 +/- 1.45 v 2.22 +/- 0.87, P <.001) as was elastic modulus (0.38 +/- 0.18 v 0.24 +/- 0.10 N/m(2), P <.001). Obese girls with insulin resistance (ie, in the highest tertile of HOMA, >3.7) had increased aortic stiffness (3.79 +/- 2.25) compared to obese girls in the lowest tertiles of HOMA (2.67 +/- 1.09, P =.045), even after adjustment for traditional cardiovascular risk factors (P =.031). The present findings suggest that preclinical changes in the aortic elastic properties are detectable in obese children. Insulin resistance seems to play an important role in the increased rigidity of the aortic wall in obese girls.