Metabolic syndrome (MS) is amajor problem in the population of children and adolescents. Genetic predisposition and environmental factors, such as physical inactivity and increased caloric intake, are responsible for the susceptibility to the development of the metabolic syndrome. Immunological aspects of obesity and MS, including the role of T regulatory cells, are also being investigated. The metabolic syndrome is defined as a cluster of risk factors (including abdominal obesity, dyslipidemia, insulin resistance, glucose intolerance or diabetes mellitus and hypertension) which increase the risk of accelerated development of cardiovascular diseases and other medical consequences.