The concern on lateral pelvic lymph node metastasis in rectal cancer has become increasingly important as this appears one of the prevalent sources of local recurrence after optimized surgery and (neo)adjuvant treatments. This randomized trial was conducted in Japan, where lateral lymph node dissection in locally advanced rectal cancer has been historically more common than radiotherapy and utilized modern MR imaging. Apart from its primary goal of comparing total mesorectal excision alone or associated with lateral lymph node dissection this trial provides contemporary data on the incidence of lateral lymph node metastasis undetected on pretreatment MR.