Cytokine-mediated immunity plays a dominant role in the pathogenesis of various immune diseases, including asthma. The recent identification of the family interleukin (IL)-1-related cytokine IL-18 now contributes to our understanding of the fine-tuning of cellular immunity. IL-18 can act as a cofactor for Th2 cell development and IgE production and also plays an important role in the differentiation of Th1 cells. Recent work identified an IL-18 association with the pathogenesis of asthma, wherein increased IL-18 expression was found in the serum of patients. Furthermore, IL-18 polymorphisms with susceptibility to asthma were reported, suggesting that IL-18 may be therapeutically relevant to asthma. In this review, we discuss the role of IL-18 in the pathogenesis of asthma and its therapeutic potential based on current research.