In recent years it has been claimed that Norwegian children and youth have reduced their level of physical activity and fitness. The aim of this systematic review was to investigate whether the amount of physical activity or level of physical fitness have changed among Norwegian children and youth during the past decades. We searched for relevant information in databases and reference lists and established contacts with scientists working in this field. The quality of the studies was evaluated on the basis of selection bias, information bias and adequate reporting of results. Five repeated cross-sectional studies of healthy boys and girls in the period from 1950 to 1997 were included. Three are based on tests of physical fitness and two of self-reported physical activity. The studies indicate that the physical fitness of the older boys has been reduced, the level of activity has been lowered, the percentage of inactive youth has increased and there are now larger variations in physical fitness. We conclude that there seems to be a negative trend in the level of physical fitness and physical activity of children and youth. This shows the need for interventions. The need for standardised parameters for physical activity is apparent.