OBJECTIVE: The number of lymph nodes retrieved is recognized to be a prognostic factor of Stage II colorectal cancer. However, the prognostic significance of the number of lymph nodes retrieved in Stage III colorectal cancer remains controversial. METHODS: The relationship between the number of lymph nodes retrieved and clinical and pathological factors, and significance of the number of lymph nodes retrieved for prognosis of Stage II and III colorectal cancer were investigated. A total of 16 865 patients with T3/T4 colorectal cancer who had R0 resection were analysed. RESULTS: The arithmetic mean of the number of lymph nodes retrieved of all cases was 20.0. The number of lymph nodes retrieved were varied according to several clinical and pathological variables with significant difference, and the greater difference was observed in scope of nodal dissection. Survival of Stages II and III was significantly associated with the number of lymph nodes retrieved. Five-year overall survival of the patients with ≤ 9 of the number of lymph nodes retrieved and those with >27 differed by 6.4% for Stage II colon cancer, 8.8% for Stage III colon cancer, 12.5% for Stage II rectal cancer and 10.6% for Stage III rectal cancer. With one increase in the number of lymph nodes retrieved, the mortality risk was decreased by 2.1% for Stage II and by 0.8% for Stage III, respectively. The cut-off point of the number of lymph nodes retrieved was not obtained. CONCLUSIONS: The number of lymph nodes retrieved was shown to be an important prognostic variable not only in Stage II but also in Stage III colorectal cancer, and it was most prominently determined by the scope of nodal dissection. A cut-off value for the number of lymph nodes retrieved was not found, and it is necessary to carry out appropriate nodal dissection and examine as many lymph nodes as possible.