Adult onset Still's disease is a systemic disorder of unknown etiology. The diagnosis is difficult and based upon Yamaguchi's criteria after exclusion of infectious diseases, hematologic process or autoimmune diseases. Clinical manifestations are various. Functional prognosis depends essentially on articular involvement. Vital prognosis depends on either hepatic failure or hematological or infectious complications, or amyloidosis. Ferritinemia is an important biological parameter which is not included in current criteria. Treatment is not well codified but steroids represent the most efficient therapy to control fever and systemic manifestations. Search for new treatments and specific markers of adult onset Still's disease are needed.