Adult onset Still's disease (AOSD) is a clinical syndrome with multiple organ failure. The patients normally show intermittent high fever for a long time, a transient rash, arthritis or joint pain as the main performance, accompanied by an increase in granulocytes and enlargement in liver, spleen and lymph node. A 71-years-old female patient with type 2 diabetes admitted hospital because of high fever, skin rash, joint pain and increased granulocyte. After review of the iron protein, she was diagnosed as AOSD. We found that clinicians need to improve the understanding for this disease in order to make the early diagnosis, especially in elderly patients with diabetes mellitus. In such patients, ferritin may not be high at early time. However, when the symptoms and signs are consistent with clinical manifestations, and anti-infection treatment effect is poor, we should pay attention to the disease, and repeated review of ferritin is necessary to assist the early diagnosis.