Although etiology of juvenile idiopathic arthritis (JIA) is currently not known, better understanding of immunologic pathways of inflammation and the development of new therapies with biologic agents have remarkably improved the treatment of JIA. However, approximately 30% of the patients with JIA do not seem to response adequately to conventional anti-rheumatic drugs but the arthritis runs a continuously active course and may lead to the evolution of erosions. Such patients benefit from biologic agents, of which the longest clinical experience comes from anti-TNF therapies. Molecules targeting IL-1, IL-6 and B- and T-lymphocytes are also used in the treatment of severe JIA.