Serum HMGB1 levels in AOSD patients were higher than those in healthy controls and correlated with CRP levels and the systemic score. Levels of serum HMGB1 were also found to decrease after the patient’s disease activity subsided. HMGB1 presented in the NETs of patients with skin lesions and high fever of AOSD patients. The gene discussed is CRP; the disease is adult-onset Still disease.