Juvenile idiopathic arthritis (JIA) is not a disease but an umbrella term that gather all forms of chronic arthritis of unknown origin and with onset in childhood. Some of these disorders appear to be the childhood equivalent of adult diseases and share therefore the same therapeutic targets. A form characterized by early onset and antinuclear antibody positivity seems to be specific for children but further evidence is needed. Systemic JIA (sJIA), although equivalent to adult onset Still disease is much more frequent in childhood. Novel potential targets for sJIA as well as for macrophage activation syndrome, its more severe complication, have therefore been investigated mainly in children.