The levels of S100A8/A9 in AOSD patients (15.43 ± 7.3 μg/mL) were higher than those of RA patients and HCs (4.04 ± 4.18 μg/mL, p < 0.001; 2.01 ± 1.06 μg/mL, p < 0.001, respectively). Here, S100A8 is linked to adult-onset Still disease.