OBJECTIVE We aimed to assess physical activity (PA) in children with juvenile idiopathic arthritis (JIA) compared with healthy peers and to determine factors influencing PA level. METHODS This was a cross-sectional study of the measured level of PA in children with JIA, compared with age- and gender-matched healthy schoolchildren. PA was estimated using a physical activity questionnaire for children and for adolescents (cPAQ/aPAQ). Disease activity was evaluated with the Juvenile Arthritis Disease Activity Score (JADAS). Functional ability was assessed with the Childhood Health Assessment Questionnaire (CHAQ). RESULTS A total of 55 children with JIA and 55 healthy control schoolchildren were included. Children with JIA had significantly lower levels of PA compared with their healthy peers as assessed with the cPAQ/aPAQ (P=0.0121). In total, 76% of the JIA group spent the day sleeping and sitting, which was significantly higher compared with the reference group (P=0.001 and P=0.055, respectively). Low PA level was associated with systemic JIA (P=0.002, OR=2.123), polyarticular JIA with positive rheumatoid factor (P=0.001, OR=2.014), JADAS-27≥6 (P=0.001, OR=2.524), patients undergoing treatment (P=0.001, OR=1.271), and higher CHAQ (P=0.002, OR=2.461). CONCLUSIONS Children with JIA were less physically active than their healthy peers and less active than recommended for general health.