Obesity and overweight are a pandemic phenomenon in the modern world. Childhood and adolescent obesity often ends up in obesity in adults. The costs of obesity and its consequences are staggering for any society, crippling for countries in development. The etiology is complex, but most often idiopathic. Hormonal, syndromic and medication-induced obesity are well investigated. Genetic causes are increasingly described. Novel technologies such as whole exome sequencing identify ever more candidate genes influencing or causing obesity. All insights into the complex problem of obesity in a team approach to treatment: diet, psychology, medications and surgery. We briefly review epidemiology, etiology, consequences and treatment approaches in childhood and adolescent obesity, with special emphasis on emerging knowledge of its genetics.