Analysis of rectus femoris samples from chidren with obesity and normal weight. Obese children display insulin resistance (IR) and other metabolic abnormalities at higher rates than do normal weight children. Results provide insight into the molecular mechanisms underlying the pathogenesis of childhood obesity. Overall design: We recruited Caucasian children, aged 6–12 years, undergoing abdominal surgery in the Pediatric Surgery Unit of the Hospital Reina Sofía (Cordoba, Spain) with a diagnosis of hernia or false positive diagnosis of acute appendicitis. Children with obesity and normal-weight were categorized according to Cole et al. (BMJ 2000, 320, 1240–1243). All children were in the prepubertal period based on the Tanner criteria (Tanner I) (Tanner et al. Archives of disease in childhood. 1976;51(3):170-9.) and as validated by plasma sex hormone concentrations. The inclusion criteria were a good state of health, age between 5 and 14 years and the absence of endogenous obesity. Exclusion criteria were disease or malnutrition and the use of a medication that alters blood pressure or glucose or lipid metabolism. The children’s parents or guardians were informed about the purpose and procedures of the study before written consent was obtained, and all children agreed to participate. The protocol was performed in accordance with the Revised Declaration of Helsinki and following the recommendations of the Good Clinical Practice of the European Union (document 111/3976/88 July 1990) and legal in-force Spanish regulations, which regulate clinical investigation in human beings (RD 223/04 about Clinical Assay), as approved by the Ethics Committees of all participants’ institutions.