|Background: In the primary analysis of JCOG0212, noninferiority of TME alone to TME with nerve-preserving lateral dissection was not confirmed and TME alone was inferior to TME with lateral dissection in the local recurrence rate. Based on these results, it was concluded that lateral dissection should be the standard treatment (Ann Surg 2017, in press).Objective: In this study, we examine the optimum range of lymph node dissection from the patterns of lymph node metastasis and the indication for perioperative treatment from the patterns of recurrence in patients with advanced lower rectal cancer who did not receive preoperative treatment in our department. Subjects: Out of 948 patients with Stage I-III lower rectal cancer (preoperative depth of invasion: T2-4), 509 patients treated with lateral dissection (53.7%) were included in this study. Patients who underwent preoperative chemotherapy or radiotherapy were excluded.Results: Among the patients treated with lateral dissection, 100/153/256 patients were pStage I/II/III, respectively. Mesenteric lymph node metastasis was observed in 169 patients and lateral lymph node metastasis was observed in 87 patients. The ratios of pathologically positive lateral lymph node metastasis were 3.9/15.0/62.9% in patients with negative lymph node metastasis/positive mesenteric lymph node metastasis/positive lateral lymph node metastasis on preoperative diagnosis, respectively. Lateral lymph node metastasis was observed in 72 out of 382 patients who underwent bilateral dissection, ten of whom (13.9%) had bilateral metastases. In the multivariate analysis, depth of invasion, lymphatic invasion, venous invasion, mesenteric lymph node metastasis, and lateral lymph node metastasis were identified as recurrence risk factors. The 5-year relapse-free survival rates were 83.2/62.3/29.4%, the 5-year cumulative local recurrence rates were 2.4/7.7/35.6%, and the 5-year cumulative distant recurrence rates were 12.6/31.9/57.4% in the patients with pathologically negative lymph node metastasis/positive mesenteric lymph node metastasis/positive lateral lymph node metastasis, respectively.Conclusion: Based on the accuracy of preoperative imaging diagnosis, the ratio of bilateral metastases, it is considered that bilateral dissection is necessary even if lateral lymph node metastasis is not suspected preoperatively. Surgical treatment alone is highly likely to be insufficient in patients with suspected lateral metastasis on preoperative imaging. Further clinical trials (JCOG1310, JCOG1410 A, Post-JCOG0212) are important to clarify the significance of lateral dissection in multidisciplinary treatment. Also, the deployment of bilateral dissection procedure into minimally invasive surgery is another future challenge.