Obesity is a serious health problem responsible for lipid and carbohydrate metabolism disorders, metabolic syndrome, hypertension, fatty liver and endocrine disorders, which are increasingly common in the paediatric population. Insulin resistance is the underlying cause of these complications. It is described as a state of reduced target tissue sensitivity to insulin despite its normal or increased serum levels. The hyperinsulinaemic-euglycemic clamp is the “gold standard” in the diagnosis of insulin resistance, but since it is time-consuming, costly and technically challenging, the method is used only in scientific research. There are several simple, indirect indicators to assess insulin resistance, which are estimated from fasting glucose and insulin values or from the data obtained in the oral glucose tolerance test, with homeostasis model assessment of insulin resistance (HOMA-IR) being the most popular tool. Despite many clinical trials, there are still no clear standards for the diagnosis and treatment of insulin resistance in children and adolescents. The management is based on the principles of a healthy lifestyle. A properly balanced diet, increased physical activity and weight loss contribute to improved insulin sensitivity. Health education, as well as prevention and treatment of childhood obesity seem to be crucial for preventing insulin resistance and related complications.