Background: This study assessed the optimal timing of computed tomography for detection of metastatic disease in locoregional lymph nodes in patients with rectal cancer who have undergone chemoradiotherapy. Materials and Methods: This observational retrospective study was performed in a single institution. All patients with locally advanced rectal cancer treated with chemoradiotherapy, followed by a total mesorectum excision from January 1, 2003 to December 31, 2012, were included. Lymph node metastases evident on preoperative computed tomography were compared with postoperative pathologic lymph node status. Results: The study population consisted of 108 patients: Group A (nodal negative on preoperative computed tomography, n = 52) and Group B (nodal positive on preoperative computed tomography, n = 56). Analysis of the computed tomography scans in Group A revealed a high ability (98.07%) to predict negative lymph nodes, compared to 58.92% for predicting positive lymph nodes in Group B. Conclusion: The results of this study suggest that the optimal timing of computed tomography for assessing lymph nodes after neoadjuvant chemoradiotherapy for rectal cancer is after 6 weeks; this timing might be key for prediction of complete clinical responses.