There were correlations between serum HMGB1 levels and phenotypes of anti-AChR antibody-positive MG: patients with generalised MG showed higher HMGB1 levels than those of patients with ocular MG (p=0.059) and controls (p=0.002); patients with thymoma showed higher HMGB1 levels than those without thymoma (p=0.094) and controls (p=0.001).