This study compared aerobic capacity and highest work load completed by children with juvenile rheumatoid arthritis (JRA) and healthy children during bicycle ergometer exercise. A secondary purpose was to determine the relationship between measures of disease severity and (a) aerobic capacity and (b) highest work load completed among the JRA patients. Aerobic capacity was measured using an open-circuit computerized gas analysis system. Sixteen patients with JRA and 16 healthy children were matched for age, sex, and body surface area. The healthy children achieved a significantly higher aerobic capacity than their respective control (p < 0.001, paired t test, two-tailed). The healthy children were able to complete higher work loads than their respective control (p < 0.01, Wilcoxon matched-pairs signed-rank test). There was no relationship between measures of articular disease severity and (a) aerobic capacity and (b) highest work load completed among the JRA patients. Results of this study provide specific direction to clinicians to initiate aerobic conditioning programs for children with JRA soon after diagnosis. Additionally, an individual's functional exercise capacity is not directly related to the severity of the articular disease.