Background: Juvenile obesity is associated with multiple cardiometabolic comorbidities, which may culminate in the metabolic syndrome (MetS). Methods: Based on a narrative review, the current knowledge of prevalence and the underlying metabolic principles regarding juvenile obesity and MetS are summarized to compile up-to-date information. In addition, the role of lifestyle as well as positive and negative influencing factors are focused on. Results: The prevalence of MetS occurs between 1 and up to 23% in the total pediatric population and in up to 60% amongst the obese and overweight. It can be considered as the consequence of multiple processes in terms of lifestyle, perinatal programming, and (epi-)genetic pathways; however, the complex underlying mechanisms and their interplay are not completely understood. Conclusion: Besides preventive approaches, the growing number of obese children and youth as well as its consequences call for effective and lasting therapeutic measures.