Chronic inflammation severely increases the risk for cancer development as seen in patients with inflammatory bowel disease (IBD). Although the exact mechanisms of inflammation-associated tumor development remain to be shown, a role for the adaptive immune system has been implicated in colitis-associated cancer (CAC). In fact, CD4+ effector T cells, which promote chronic inflammation in IBD, create a tumor convenient environment, which can lead to cancer initiation, promotion, and progression. Thereby, the cytokines interleukin-6 and tumor necrosis factor-alpha constitute an important link between inflammation and tumor growth. Furthermore, cytotoxic CD8+ T cells, which usually are protective as part of the host antitumor immune response in sporadic cancer, can contribute to the aggravation of chronic inflammation and thereby support tumor development. In contrast, regulatory T cells, which have been shown to attenuate tumor immunosurveillance, act as potent suppressors of chronic inflammation and thus can have protective effects in CAC. This review discusses the role of the adaptive immune response and especially T cells in the pathogenesis CAC and possible implications for the therapeutic applications.