Results: Overall, miR-155 and miR-21 were significantly over-expressed in both non-neoplastic and neoplastic mucosa of IBD patients as compared to healthy controls. MiR-155 alone was preferentially expressed in MSI vs. MSS IBD-CRCs. In contrast, miR-155 was poorly deregulated in non-neoplastic and neoplastic tissues of non-IBD MSI or MSS CRCs. Conclusion: miR-155, alone or synergistically with miR-21, may favor the emergence of MSI IBD-CCRs. Since its deregulation was not limited to neoplastic tissues but extends to non-neoplastic normal mucosa as well, the hypothesis of a miR-155 field defect promoting MMR deficiency and yet MSI-driven transformation can be proposed.