PURPOSE: To retrospectively analyze the MR imaging features of rectal cancer in patients with inflammatory bowel diseases (IBD). MATERIALS AND METHODS: The MR imaging examinations of 13 patients with IBD-related rectal cancer were retrospectively reviewed. MR imaging included T2-weighted, diffusion-weighted (DW), and gadolinium chelate-enhanced MR imaging. MR imaging findings were analyzed and compared with endoscopic and histopathological findings. RESULTS: Eight patients (8/13; 62%) had active IBD and five (5/13; 38%) had quiescent IBD on MR imaging. Two different tumor patterns were individualized including clearly visible soft-tissue mass (4/13; 31%) (Type 1 tumor) and marked circumferential rectal wall thickening (9/13; 69%) (Type 2 tumor). Twelve tumors (12/13; 92%) showed high signal intensity on T2-weighted MR images. All six tumors studied with DW-MR imaging (6/6; 100%) showed high signal on DW-MR imaging with restricted diffusion on apparent diffusion coefficient (ADC) map. On gadolinium chelate-enhanced MR imaging, heterogeneous enhancement was observed in one tumor (1/13; 8%), whereas 12 tumors (12/13; 92%) showed homogeneous enhancement. MR imaging showed pelvic fistula and intrapelvic abscess in association with four (4/13; 31%) and two tumors (2/13; 15%), respectively. CONCLUSION: Our limited retrospective study demonstrates that rectal cancer in IBD patients can present as a circumferential wall thickening resembling inflammation and can occur in the absence of fistula or abscess. The use of T2-weighted and DW-MR imaging is recommended to improve rectal cancer detection in patients with long-standing IBD.