The etiology of AOSD is unknown, but the following are recognized as central to the pathogenesis of AOSD: an abnormal activation of innate immune cells (e.g., neutrophils, monocytes, and macrophages) and the overproduction of cytokines such as interleukin (IL)-1β, IL-6, tumor necrosis factor-alpha (TNF-α), and IL-18 (1–4). Here, IL18 is linked to adult-onset Still disease.