This study compares levels and patterns of objectively assessed physical activity in Sweden and the United States by using identical accelerometer metrics. Data of adult respondents with > or =4 days with > or =10 hours per day of accelerometer wear from Sweden (2001-2002, n = 1,172) and the United States (2003-2004, n = 2,925) were compared. Outcomes reported by age and body mass index within sex include accelerometer counts per minute and amounts and bouts of activity at different intensities, that is, sedentary, low, lifestyle, and moderate or higher intensity physical activity. The mean counts per minute were 375 (95% confidence interval (CI): 360, 390) and 377 (95% CI: 363, 391) for Swedish and US males, respectively, and 363 (95% CI: 347, 379) and 298 (95% CI: 289, 307) for Swedish and US females. Older respondents and those with higher body mass index had lower activity levels. Swedish and US males spent 36 (95% CI: 34, 38) and 33 (95% CI: 31, 36) minutes per day, and Swedish and US females spent 32 (95% CI: 29, 34) and 19 (95% CI: 17, 21) minutes per day in moderate or higher intensity physical activity. Older Swedes were more active in moderate or higher intensity activities than were older US respondents. However, younger Swedish males had more sedentary behavior time than did younger US males. These results provide a framework for international comparisons of physical activity levels and patterns, and they represent strong evidence for the importance of investment in objective measurement of physical activity.