 A randomized withdrawal study in which responders to open-label treatment with tofacitinib will be randomized in a 1:1 ratio to tofacitinib or placebo in a double-blind phase. In the double-blind phase time to sJIA flare will be evaluated as primary endpoint and subjects will be discontinued once they experience sJIA flare. Once 31 flares are reported the study will be completed. 