Objective: To examine habitual physical activity, aerobic capacity, adiposity, and dynamic balance skills in children with JIA, inclusive of knee involvement, compared to age and sex matched healthy controls. Design: Cohort study with a matched-pair design Participants: Twenty-five youth with JIA, ages 10-20, (16 female, 9 male) were matched by age and sex to 25 healthy control participants. Methods: Physical activity data was collected using an ActiGraph accelerometer for 7 days. Aerobic capacity (relative VO2peak) was assessed by a maximal bike test. Adiposity (fat mass index) was evaluated by dual energy X-ray absorptiometry (DXA). Three dynamic balance tests examined balance performance. Results: No significant difference between groups was found in any of the outcomes after adjusting for multiple comparisons. Conclusions: Youth with JIA have similar physical activity, aerobic fitness, adiposity, and functional balance ability as their healthy peers. Differences found in physical activity between male groups could have clinical significance.