N eoadjuvant chemoradiotheraphy (CRT) improves tumor downstaging, pathological complete response (pCR), and local control (1, 2). pCR rates of 13%-30% have been reported in phase II and phase III trials following 5-fluorouracil-based preoperative CRT (3, 4). Currently, management of patients with clinical complete response (cCR) remains controversial (5-8).A recent meta-analysis including 218 phase I/II or retrospective studies and 28 phase III trials of adjuvant CRT reported that T3 rectal cancer is associated with high local recurrence rates after nonsurgical treatment (9). In addition, similiar results were recently shown from a study using a "wait-and-see" policy after CRT (10).Accurate imaging methods are needed to evaluate CRT responses, and post-CRT magnetic resonance imaging (MRI) is frequently used for this purpose. However, the method has low accuracy in predicting the pathological stage of the tumor and can often overstage T1 and T2 tumors due to the limited capability of MRI to differentiate viable tumor, residual fibrotic nontumoral tissue, and a desmoplastic reaction. Understaging of irradiated rectal cancer can affect treatment planning, including the surgical strategy, and thus affects the tumor recurrence rate and prognosis (11).Diffusion-weighted (DW)-MRI is a functional imaging technique that yields qualitative and quantitative information and provides unique insights regarding tumor cellularity, integrity of cell membranes, and microcirculation.