The Norwegian physical activity recommendations for children and youth state that there should be a minimum of 60 min of physical activity of at least moderate intensity every day. The purpose of this study was to evaluate objectively the level of physical activity in a representative cohort of urban children and youth in Norway with regard to these recommendations. Four hundred and ten 9-year-old and 350 15-year-old boys and girls from the Oslo region participated. Physical activity was registered for 4 consecutive days using the Computer Science and Application activity monitor. The results showed that 86.2% of the 9-year-olds and 55.4% of the 15-year-olds met the recommendations. Furthermore, the activity level was significantly (P< 0.0001) higher among boys than girls of both age groups and significantly (P<0.001) lower in the oldest cohort than in the youngest one. All participants were less active during the weekend than during the weekdays (P< 0.05). In conclusion, a number of urban children and youth do not fulfill the Norwegian physical activity recommendations, especially among the 15-year-olds. It is therefore important to provide action towards those children and youth who are least physically active and simultaneously prevent the general decline in physical activity.