BACKGROUND: It is important to understand the correlates of physical activity in order to influence policy and create environments that promote physical activity among preschool children. We compared preschoolers' physical activity in Swedish and in US settings and objectively examined differences boys and girls indoor and outdoor physical activity regarding different intensity levels and sedentary behaviour. METHODS: Accelerometer determined physical activity in 50 children with mean age 52 months, (range 40-67) was recorded during preschool time for 5 consecutive weekdays at four sites. The children wore an Actigraph GTIM Monitor. RESULTS: Raleigh preschool children, opposite to Malmo preschoolers spent significantly more time indoors than outdoors (p