The rectum is a pelvic organ, complex in its morphology and its topographic relationships. Its double embryologic origin explains the two types of tumors that develop in the rectum: (1) lieberkühnian adenocarcinoma in the pelvic rectum and (2) squamous epithelioma in the anal canal. Its venous and lymphatic supply, intensively developed, realizes early pathway of tumoral dissemination. The pelvic relationships of the rectum and anus explain the technical difficulty of rectal surgery, especially when subperitoneal resection and anastomosis are concerned. Imaging of this area permits an early diagnosis of rectal tumors and allows a less invasive surgery with a carcinologic precision.