Diseases such adult Still's disease (normal ferritin, absence of sore throat and organomegaly, and inconsistent rash), brucella (brucella tube agglutination negative), ANCA-associated vasculitis (ANCA negative, no pulmonary involvement, normal urinary sediment, and no asthma history), systemic lupus erythematosus (ANA negative, anti-ds-DNA negative, normal complement level, and no hematologic or renal involvement) were considered in the differential diagnosis, and relevant investigations were conducted. The gene discussed is BTG3; the disease is adult-onset Still disease.