The prevalence of risk factors at developmental age shows a growing tendency. This exerts an effect on the development of chronic diseases at adulthood, especially cardiovascular diseases, which constitute the most important health problem. The objective of the study was evaluation of the dietary habits and identification of the prevalence of overweight and obesity in a sample of 5th-grade pupils in a randomly selected elementary school in Sieradz. The study was conducted in 2007 and covered 160 pupils (79 girls and 81 boys). The research tool was an anonymous survey questionnaire dealing with nutrition and physical activity. Measurements of height, body mass, waist circumference and hip circumference were performed. BMI and WHR were calculated. The results were assessed with the use of centile grids adjusted for sex and age. It turned out that as many as 25% of children under study had an excessive body weight (23% of girls and 28% of boys). Overweight was more prevalent than obesity; 19% of boys were overweight and 9% obese, whereas the situation was different among girls – 9% of them were overweight and 14% obese. Every tenth child in the study had incorrect waist circumference, which is associated with an increased risk of CVD. Every fourth 11-year-old had problems with maintaining correct body mass. This is related to an inadequate diet and low physical activity. There is a need for health education among pupils and their parents in the field of adequate nutrition and physical activity. Preventive actions should be popularised in order to decrease the prevalence of risk factors of chronic diseases at the developmental age.