Excessive amount of adipose tissue in children and adolescents and simple obesity in particular constitute a growing health problem throughout the world. Adverse health effects of obesity of children justify the need to look for efficient treatments, among them the dietary treatment. THE AIM OF THE STUDY was to examine the effectiveness of dietary treatment in children with simple obesity on the basis of thorough analysis of their state of nutrition, method of nutrition and eating habits and the impact of other environmental factors. Four research hypotheses were formulated: 1. simple obesity of children is influenced by selected environmental factors such as parents' level of education, familial inclination to obesity and health habits, 2. chosen and accepted by the child and/or its mother/parents programme of dietary treatment in the form of low-energy diet with elements of low glycemic index results in the loss of body mass in children, 3. implemented dietary treatment translates into the modification of basic anthropometric features--body mass, body height, thickness of skin and adipose folds on arm, below shoulder blade (scapula), on abdomen as well as arm circumference and anthropometric parameters of examined children--body mass index BMI, waste-hip ratio, body fat content, 4. implemented dietary treatment has an impact on modification of certain biochemical indicators--lipid profile of children with increased indicators of lipid metabolism.