The purpose of this study was to determine whether multiplanar reconstruction (MPR) images can improve the accuracy of MDCT-based colorectal cancer preoperative staging by receiver-operating characteristic (ROC) analysis. Fifty-five patients with colorectal cancer underwent contrast-enhanced CT colonography using an 8- or 16-row scanner. Two separate interval reviews of the axial MDCT datasets with/without MPR images (coronal and sagittal) were performed independently by two radiologists blinded to both the colonoscopic and histopathologic results. At each review session, the radiologists were asked to determine the colorectal cancer TNM stage within the context of differentiating < or =T3 from T4, N0 from > or =N1 and M0 from M1 using a five-point confidence scale. The radiologists' performance for staging the colorectal cancer using axial CT datasets with/without MPR images was evaluated using ROC analysis. Sensitivities, specificities and interobserver agreement were assessed. When MPR images were added, significant improvement was achieved by both radiologists for differentiating N0 from > or =N1 in terms of both A(Z) (0.651 to 0.769; 0.573 to 0.713) and specificity (26.7 to 69.2%; 23.1 to 76.9%) (P<0.05). For T staging, ROC analysis failed to show a significant improvement in terms of differentiating < or =T3 from T4 for either radiologist (P>0.05), but a significant improvement in the specificity (70 to 90%; 80 to 92%) was achieved by one radiologist (P<0.05). In terms of the M staging, a significant improvement in the Az (0.844 to 0.996) was observed for the combined interpretation of the axial and MPR images by one radiologist (P<0.05). Furthermore, substantial or almost perfect interobserver agreement was achieved for all TNM stagings for the combined interpretations (kappa=0.641-0.866), whereas only fair to substantial agreement was achieved for the axial images alone (kappa=0.337-0.707). In conclusion, the combined interpretation of the axial and MPR MDCT images significantly improved the local staging of colorectal cancer compared with assessments based on axial images alone.