Local recurrence of rectal adenocarcinoma is mainly due to failure to remove all the tumour. A method is described for the routine detection of involvement of the circumferential (lateral) resection margin. Current definitions of the length of the rectum are inadequate for the assessment of the risk of local recurrence as the rectum frequently extends higher than 15 cm. Use of the term recto-sigmoid should be replaced clinically by sigmoidoscopic measurement of the height of a tumour and pathologically by its anatomical relationship to the level of peritoneal reflection, i.e. lower or upper segment of the rectum or the sigmoid colon. Tumours above the peritoneal reflection (upper segment) are at risk of circumferential resection margin involvement due to their retroperitoneal component. The amount of tissue excised varies considerably from surgeon to surgeon. Meticulous attention to the clearance of the tumour at the circumferential resection margin is essential if local recurrence rates are to be reduced. A trial of postoperative radiotherapy should be instigated based on the pathologist's identification of patients at high risk of local recurrence.