Background: Obesity is characterized by chronic inflammation, immune dysregulation, and alteration of gene expression, associated with type 2 diabetes mellitus and cardiovascular disease. The degree to which these changes occur in childhood obesity is not fully defined. Aims and Methods: The aim was to investigate the effect of childhood obesity on immune cell frequency, macrophage activation, cytokine production, and specific regulators of metabolic gene expression. Profiling was performed on peripheral blood from 29 obese and 20 nonobese children using real-time PCR, ELISA, and flow cytometry. Results: Fasting glucose was similar in both groups, but there was a higher degree of insulin resistance in obese subjects (homeostasis model of assessment for insulin resistance, 4.8 vs 0.84; P .001). Soluble CD163, a marker of macrophage polarization to a proinflammatory profile, was elevated in the obese compared to nonobese children (135 vs 105 ng/mL; P .03). Invariant natural killer T cells were reduced in the obese children (CD3 T cells, 0.31 vs 0.53%; P .001). Cytokine profiling revealed significantly elevated TNF- (6.7 vs 5.1 pg/mL; P .01) and leptin (1186 vs 432 pg/mL; P .001) and reduced adiponectin (884 vs 1321 pg/mL; P .001) in obese compared to nonobese children. Stimulation of peripheral blood mononuclear cells from obese children resulted in higher levels of IL-1 (2100 vs 1500 pg/mL; P .018). There was a 4-fold increase in expression of microRNA33a (P .001) and a 3-fold increase in microRNA33b (P .017) in obese children. Conclusion: Childhood obesity is associated with changes in immune cell frequency, inflammatory environment, and regulation of metabolic gene expression. These changes have been causally linked to the onset of metabolic disease in adulthood and suggest the future trajectory of obese children to the development of type 2 diabetes mellitus and premature cardiovascular disease