An intussusception due to colonic adenocarcinoma has sometimes been reported.However,to the best of our knowledge,reports of intussusception due to rectal adenocarcinoma are extremely rare.In this report,the case of a young man with rectal adenocarcinoma causing intussusception is described.A 24-year-old man visited a hospital complaining of abdominal pain,and an upper rectal cancer was diagnosed by colonoscopy.Computed tomography showed intussusception caused by a large tumor in the pelvis and absence of distant metastases.Locally advanced rectal cancer causing intussusception was diagnosed,and a low anterior resection was performed.Intraoperatively,repair of the invagination could not be accomplished easily;therefore,the repair was abandoned.Instead,the tumor was removed en bloc to avoid dissemination of the cancer.Histopathologically,the tumor was diagnosed as a poorly differentiated adenocarcinoma,pStageⅡA.The patient has no evidence of recurrence at 10 mo after the operation. An intussusception due to colonic adenocarcinoma has sometimes been reported. Host to the best of our knowledge, reports of intussusception due to rectal adenocarcinoma are extremely rare. In this case, a case of a young man with rectal adenocarcinoma causing intussusception is described. A 24-year-old man visited a hospital complaining of abdominal pain, and an upper rectal cancer was diagnosed by colonoscopy. Computed tomography showed intussusception caused by a large tumor in the pelvis and absence of distant metastases. Locally advanced rectal cancer causing intussusception was diagnosed , and a low anterior resection was performed. Intraoperatively, repair of the invagination could not be accomplished easily; therefore, the repair was abandoned. Instead, the tumor was removed en bloc to avoid dissemination of the cancer. Histopathologically, the tumor was diagnosed as a poorly differentiated adenocarcinoma, pStageⅡA.The patient has no evidence of recurrence at 10 mo after the operation.