Overweight in childhood is a problem that threatens health and quality of life in the future. It results from a long-term caloric imbalance in which the intake of calories is greater than their consumption. Genetic factors, habits, metabolism and environmental factors are important in developing overweight. Genetic counselling and certain tests to diagnose the syndrome are only necessary if certain symptoms and signs point to a possible syndromic cause. In this case, extreme overweight appears already in the early years, and the outcome is better if the diagnosis is made as early as possible to prevent other, serious consequences. When the cause of overnutrition is an endocrine disorder, although this is not a common situation, growth retardation is usually observed. The most common causes of being overweight are environmental factors and acquired habits, increased calorie intake and insufficient physical activity. In addition to the fact that obesity affects the quality of life, it also affects psychosocial development, so psychological assessment and counselling of children and adolescents, as well as families, is an important approach to treatment. A therapeutic approach to obesity should include a multidisciplinary team with proper nutrition, exercise and psychological support, and the best results are achieved when the whole family is involved. Preventive programs already in childhood, which would be manifested by changes in the family's habits and, consequently, the child's habits, as well as an overall change at the population level, are essential for preventing the development of an obese population.