- For a patient enrolling into the MTX arm; a pediatric patient diagnosed at any time with moderately to severely active polyarticular or polyarticular-course JIA (defined as arthritis affecting >= 5 joints at the time of diagnosis of polyarticular or polyarticular-course JIA) who is prescribed MTX therapy alone or in combination with other disease modifying anti-rheumatic drugs (DMARDs) according to the local product labeling (initiated treatment within 24 months of registry entry) and has received continuous therapy and the physician can available provide source documentation of SAEs, AEs of Special Interest, and dosing information since initiation of therapy.