Recent studies that have evaluated the immunologic factors that mediate the development of the two forms of inflammatory bowel disease, namely Crohn's disease and ulcerative colitis (UC), have suggested that these diseases are because of disparate immune responses. Although Crohn's disease has been characterized as a dysregulation of the T helper (Th)1/Th17 pathways more recent evidence has emerged that UC pathogenesis is associated with a nonclassical NK (natural killer) T cell producing an atypical Th2 (interleukin (IL)-13) response. In the following review the insights gained from both animal models and human studies as to the function that IL-13 and NK T cells have in the pathogenesis of UC will be discussed.