Interleukin-18 is a cytokine member of the IL-1 super family that seems to exert powerful Th1-promoting activities in synergy with IL-12. Here we describe the participation of IL-18 in inflammatory joint diseases, in particular rheumatoid arthritis, adult onset Still's disease and juvenile idiopathic arthritis. The emphasis of this study was to summarize in vivo and in vitro studies that focused the action of this pro-inflammatory cytokine on the arthritic process as well as its role in the complex network of chemical mediators involved.