The article presents a literature review which devotes to one of the major issues of healthcare today obesity in children and adolescents. The consequences of childhood obesity, methods of determination and pathophysiology of obesity are described in detail. It was considered the influence of genetic factors in the formation of obesity, the effect of intestinal microbiota in the pathogenesis of obesity. The literature search was carried out in the databases of NCBI, PubMed, PubMed Central, eLIBRARY.ru, etc. Obesity in children and adolescents is one of the most important issues for people from most countries in today's world. Worldwide, the prevalence of this pathology has increased over the past three decades. Obesity in children and adolescents is a complex, multifactorial disease in which genetic and non-genetic factors can be identified. Although the vast majority of childhood obesity incidents are exogenous, a small proportion may have endogenous causes. Currently, particular importance is attached to the study of hereditary predictors of obesity and its main complications. Being a complex and inherited trait (disease), obesity is a consequence of the interaction of genetic predisposition, epigenetics, metagenomics, and the environment. Also, recent experimental and clinical data show the importance of intestinal microbiota, which can cause overweight and obesity in some patients. Molecular genetic studies have confirmed changes in intestinal biocenosis with developing obesity in children and adolescents. Obesity, which began in childhood, causes short-term and long-term adverse effects on physical and psychosocial health and largely becomes a risk factor for the development of various metabolic disorders and cardiovascular pathology. Understanding the multifactorial mechanisms involved in the formation of obesity in children and adolescents provides opportunities for the early prevention of obesity and its complications.