Background: Reduced physical activity (PA) is associated with childhood obesity and is a target for intervention. This study aimed to assess objectively measured PA patterns in Dutch children across weight categories, age groups and gender at the start of a lifestyle intervention.Methods: 202 children with overweight and (morbid) obesity (55% girls, 12±3y of age, BMI z-score +3.15±0.73), referred to the Centre for Overweight Adolescents and Children’s Healthcare (COACH, Maastricht UMC+) were included. Children were categorized as overweight, obese or morbidly obese according to their BMI z-score. PA patterns (total PA, sedentary time (ST), light PA and moderate to vigorous intensity PA (MVPA)) werewas measured with the GT3X Actigraph accelerometer. Wear time validation was set on four days, 480 min/day, including one weekend day.Results: PA levels in children with morbid obesity were higher compared to children with obesity, also after correction for age and gender (corrected difference (B) 118 counts per minute (cpm), p=.006). Sedentary behaviour (STB) was lower in children with morbid obesity compared to children with obesity (B -51 min/day, p=.018). Girls performed significantly less moderate to vigorous MVPA than boys (B -11 min/day, p<.001) and for each year increase of age with increasing age, children performed less PA (B -46 cpm, p<.001) and STB increased (B 18 min/day, p<.001).Conclusion: Weight category morbid obesity, younger age and male gender were positively associated with PA and negatively with SB. PA and ST is different in subgroups of children with overweight and (morbid) obesity, depending on gender, age and overweight severity. In particular in older girls in the weight category ‘obesity’, levels of PA and ST are worrisome. These findings highlight the need for tailored PA promotion. Trial registration: The trial is registered with Clinicaltrials.gov NCT02091544