Understanding activity levels and body composition of children and their relationship to a healthy lifestyle is a growing area of research. There is much concern for the rate of increases seen in overweight and obese children around the world. The purpose of this study was to assess the physical activity and body composition levels of American, Swedish, and Australian children. Design: This study consisted of 711 American children, 563 Australian children, and 680 Swedish children, for a grand total of 1,954 participants. Participants wore a Yamax pedometer (MLS-2000) attached to the waistband of their pants in line with the right knee for a full day on four consecutive days. Pedometers were sealed to assure that they were not accidentally reset. Step counts were recorded on a daily basis at school. Measures of height and weight were obtained. Results: Descriptive data (means and SD) for step counts and BMI by sex, age, and country were calculated to determine activity levels and body composition. Oneway ANOVA for step counts and BMI between countries at each age and sex found that in general the Swedish children were significantly more active than the Australian and American children, and in general, the American children were significantly heavier than the Australian and Swedish children. The activity curve is somewhat level during the preadolescent years and does not show a strong decline with age. The Swedish girls are the one group where a decline in steps with age appears to be occurring. In the BMI analysis only the older American children revealed a problem with overweight. No groups were classified as obese. The rate of increase in BMI with age is much greater in the American children than in the Swedish or Australian children. Correlation analysis found very little relationship between step counts and BMI. Only 5 significant negative correlations were found between step counts and BMI, and those correlations were relatively low. This study found the American children to be the least active of the three countries and the heaviest. Their rate of increase in BMI is much greater than their counterparts in Sweden and Australia. The Swedish children are the most active group followed by the Australian's. Swedish and Australian children maintain much healthier weight throughout their prepubescent years than do the American children who have a greater percentage who are classified as overweight and who get much heavier with age.