The natural history of locally recurrent rectal cancer was analysed to assess whether preoperative irradiation altered the clinical course of the disease. In a randomized controlled trial of 849 patients, the value of preoperative radiotherapy in those with operable rectal adenocarcinoma was examined. After a minimum follow-up of 4 years, 156 patients who developed local recurrence were studied retrospectively. There were no differences concerning symptoms and the site of local recurrence between irradiated and non-irradiated patients. Curative treatment was rarely possible and median survival was only about 1 year, irrespective of adjuvant treatment. Local recurrence was the only manifestation of disease in 30-50 per cent of patients. An earlier and more aggressive surgical approach might improve survival.