Lateral pelvic lymph node dissection is still the important operation for the treatment of rectal cancer. But the experts in Europe and America hold different opinions from those in Japan on whether lateral pelvic lymph nodes should be considered as regional lymph nodes of rectal cancer and the significance of lateral pelvic lymph node dissection. Different definitions of lateral pelvic lymph nodes will lead to different staging for rectal cancer and consequently result in different treatment strategies. In different periods of time, there are evolving definitions for lateral pelvic lymph nodes proposed by the scholars in Europe and America as well as in Japan. Here, the author interprets these evolving changes based on the available data, with the emphases on evolving definitions for pelvic lateral lymph nodes of the Japanese Society for Cancer of the Colon and Rectum, because more extensive efforts have been made by Japanese scholars in this field.