The treatment of patients with a malignant rectal tumor has evolved over the past few years. The role of medical imaging techniques, notably MRI, has become increasingly important in the preoperative assessment of rectal tumors. Radiologists are finding that their presence is requested more and more frequently at multidisciplinary team meetings for decision-making on the treatment of these tumors and therefore they must have a grounding in the therapeutic issues involved. Locoregional assessment of malignant rectal tumors may be performed prior to initiating treatment or as a re-evaluation following neoadjuvant therapy. We are interested in the assessment of the initial locoregional extension of these rectal tumors and we place much emphasis on the ability to identify MRI criteria which determine the patient's prognosis and treatment. We will also examine the advantages of MRI as well as its limits in this assessment.