Obesity is associated with an increased all-cause mortality rate and even small weight losses can be associated with short-term reduction in risk factors for disease. There is strong evidence that weight loss in obese subjects improves risk factors for diabetes and cardiaovascular diseases. Metabolic syndrome (MS) in adults is defined as a cluster of risk factors for cardiovascular disease and type 2 diabetes mellitus, which includes abdominal obesity, dyslipidemia, glucose intolerance and hypertension. Application of the MS concept in children and adolescents is controversial; in fact no consensus exists on a specific definition for pediatric MS. Lack of consensus is in part due to body evolution associated with childhood and puberty that is related to changes in metabolic and clinical characteristics. The aim of this article is to try to clarify the differences between the MS as a concept and the MS as a diagnostic category, as well as to develop a theory related to its pathophysiology. We comment on the relationship between obesity, regional fat distribution and the MS, and finally we offer some insights into MS methodological approaches for estimating metabolic risk-factor clustering in children and adolescents.