Juvenile idiopathic arthritis (JIA) is a rare inflammation with still unidentified cause. It can also be cause of fever of unknown origin. Diagnosis is made by eliminating infection, malignancy, and rheumatological diseases. In this report, case of a 5-year-old patient with symptoms of intermittent fever, areas of rash on the body, itching, and swelling, redness, and pain in the right and left ankle is described. Serological test results were negative for infectious agents, and malignancy was excluded. Patient was diagnosed with systemic JIA associated with intermittent fever, negative rheumatological markers and negative serology test results. Treatment with methylprednisolone and methotrexate yielded positive clinical response. Diagnosis of systemic JIA can be challenging, and must be made by eliminating other diseases.