A random sample of 682 8- and 13-year-old children resident in Sweden was studied with regard to physical activity, energy intake, height, weight and skinfold thickness. A reduction of physical activity over the years was indicated by a tendency towards a higher body fat content in spite of a lower mean energy intake as compared with such values obtained 10-15 years ago in Swedish children of equal ages. Children characterized by high habitual physical activity tended to have a lower body fat content, despite a higher energy intake, than less active children. Children, especially girls, of parents with a low educational level showed a tendency towards higher body fat content as compared with those of parents with higher education.