The treatment of rectal cancer has changed significantly during the last 30 years. With improved surgical technique and the introduction of preoperative radiotherapy sphincter preserving surgery is now predominant and the rate of local recurrence has been reduced substantially. However, new therapy concepts may also introduce an increased risk of complications. A register to monitor quality control in rectal cancer treatment in Sweden was established in 1995. It covers over 95 per cent of the patients with rectal cancer reported to the Swedish National Cancer Registry. Collection of data and validation are done by six regional oncology centres under supervision of surgeons appointed by the hospitals involved. The results are then collated to a nationwide quality register, enabling regions to compare themselves with other regions, and hospitals with other hospitals.