Two cases of extramedullary plasmacytoma of the rectum treated by radiotherapy are reported. In one patient local control of disease was achieved at 36 months. A second patient treated by a palliative course of radiotherapy had initial good local regression and control of symptoms at 3 months. In view of the radiosensitivity of this tumour, consideration should be given to treating extramedullary plasmacytoma of the rectum by primary radiotherapy.