Regulatory T cells(T regs) are key elements in immunological self-tolerance.The number of T regs may alter in both peripheral blood and in colonic mucosa during pathological circumstances.The local cellular,microbiological and cytokine milieu affect immunophenotype and function of T regs.Forkhead box P3+ T regs function shows altered properties in inflammatory bowel diseases(IBDs).This alteration of T regs function can furthermore be observed between Crohn’s disease and ulcerative colitis,which may have both clinical and therapeutical consequences.Chronic mucosal inflammation may also influence T regs function,which together with the intestinal bacterial flora seem to have a supporting role in colitis-associated colorectal carcinogenesis.T regs have a crucial role in the immunoevasion of cancer cells in sporadic colorectal cancer.Furthermore,their number and phenotype correlate closely with the clinical outcome of the disease,even if their contribution to carcinogenesis has previously been controversial.Despite knowledge of the clinical relationship between IBD and colitis-associated colon cancer,and the growing number of immunological aspects encompassing sporadic colorectal carcinogenesis,the molecular and cellular links amongst T regs,regulation of the inflammation,and cancer development are still not well understood.In this paper,we aimed to review the current data surrounding the role of T regs in the pathogenesis of IBD,colitis-associated colon cancer and sporadic colorectal cancer. Regulatory T cells (T regs) are key elements in immunological self-tolerance. The number of T regs may alter in both peripheral blood and in colonic mucosa during pathological events. The local cellular, microbiological and cytokine milieu affect immunophenotype and function of T regs .Forkhead box P3 + T regs function shows altered properties in inflammatory bowel diseases (IBDs). This alteration of T regs function can not be observed between Crohn’s disease and ulcerative colitis, which may have both clinical and therapeutical consequences. Chronic mucosal inflammation may also influence T regs function, which together with the intestinal bacterial flora seem to have a supporting role in colitis-associated colorectal carcinogenesis. Regs have a crucial role in the immunoevasion of cancer cells in sporadic colorectal cancer. Stillrther, their number and phenotype correlate closely the clinical outcome of the disease, even if their contribution to carcinogenesis has previously been controversial.Despite knowledge of the clinical relationship between IBD and colitis-associated colon cancer, and the growing number of immunological aspects encompassing sporadic colorectal carcinogenesis, the molecular and cellular links amongst T regs, regulation of the inflammation, and cancer development are still not well understood. this paper, we aimed to review the current data surrounding the role of T regs in the pathogenesis of IBD, colitis-associated colon cancer and sporadic colorectal cancer.