SummaryBackgroundThere are no standardised criteria for the ‘regional’ pericolic node in colon cancer, which represents a major cause of the international uncertainty regarding the optimal bowel resection margin. This study aimed to determine ‘regional’ pericolic nodes based on prospective lymph node (LN) mapping.MethodsAccording to preplannedin vivomeasurements of the bowel, the anatomical distributions of the feeding artery and LNs were determined in 2996 stages I–III colon cancer patients who underwent colectomy with resection margin >10 cm at 25 institutions in Japan.FindingsThe mean number of retrieved pericolic nodes was 20.9 (standard deviation, 10.8) per patient. In all patients except seven (0.2%), the primary feeding artery was distributed within 10 cm of the primary tumour. The metastatic pericolic node most distant from the primary tumour was within 3 cm in 837 patients, 3–5 cm in 130 patients, 5–7 cm in 39 patients and 7–10 cm in 34 patients. Only four patients (0.1%) had pericolic lymphatic spread beyond 10 cm; all of whom had T3/4 tumours accompanying extensive mesenteric lymphatic spread. The location of metastatic pericolic node did not differ by the feeding artery's distribution. Postoperatively, none of the 2996 patients developed recurrence in the remaining pericolic nodes.InterpretationThe pericolic nodes designated as ‘regional’ were those located within 10 cm of the primary tumours, which should be fully considered when determining the bowel resection margin, even in the era of complete mesocolic excision.FundingJapanese Society for Cancer of the Colon and Rectum.