Obesity represents a chronic inflammatory status and adipocytes release either cytokines or an array of adipokines such as leptin, endowed with immunomodulating and systemic activities. The involvement of cytokines in obesity as well as of the adipokine leptin is supported by the notion that weight reduction normalizes mediators of inflammation. In this framework, we will demonstrate that in obese children, subjected for a period of six months to a hypocaloric diet, reduction of major biochemical and anthropometric parameters correlates with a normalization of immune status. Infact, absolute numbers of CD4+ cells and CD4/CD8 ratio increase, while leptin values fluctuate within normal ranges, being this adipokine involved in the modulation of either innate or adaptive immune responses. In the discussion, the immune abnormalities detected in obesity will be pointed out and emphasis will be placed on the increased frequency of infectious episodes occurring in obese adolescent and adults. Finally, the infectious etiology of obesity will be illustrated in the sense that adipocytes interacting with infectious agents may cause obesity. Taken together, the bulk of available data indicate that childhood obesity should be prevented or reduced to avoid more serious complications in adulthood.