While several studies have demonstrated that weight loss can improve metabolic risk factors in obese children, data regarding the effect on early vascular disease is missing. Therefore we designed this study including a cohort of obese children before and after a structured weight reduction program in order to answer the question, whether such an intervention can improve endothelial cell function and reverse an increased intima media thickness. Since each intervention program leading to body weight reduction is a severe interference with personal lifestyle, we feel that these questions need to be answered before intervention programs are initiated on a public health basis.