BACKGROUND A high level of physical fitness is associated with cardiovascular health in adolescents. We describe change in physical fitness levels assessed at two time points over 3 years. METHODS The study presents a longitudinal design, with the first phase data collection at 8 years and the second phase carried out at 11 years. A total of 516 children (254 boys) aged to 7.7±0.4 years (in 2010) and 10.9±0.4 years (in 2010) and 10.9 ± 0.4 years (in 2013) participated to the study. Cardiorespiratory fitness, muscular strength, speed, and agility were assessed in this study. For each physical fitness test, determination of the situation (in terms of percentiles) of each child in 2010 and then in 2013 compared to national standards. The 2010 and 2013 percentiles are then compared using the Wilcoxon signed rank test. RESULTS Muscular strength, agility and cardiorespiratory fitness decrease in both sex (p<0.01). A significant decrease was also found for all physical fitness components in normal weight children (p<0.05). For normal weight children in 2010 who became overweight or obese in 2013, there was a significant decrease in scores of cardiorespiratory fitness and agility tests (p<0.05). For overweight children in 2010 becoming from to normal weight status in 2013, only the agility test decreased significantly (p<0.05). Children being overweight or obese in 2010 and remaining in 2013, had a significant decrease in their physical fitness levels (p<0.05). CONCLUSIONS Our results indicate that the physical fitness of French youth decrease between childhood and early adolescence. Developing and introducing a health promotion curriculum in the French schools is suggested to improve health and physical fitness.