Surgery is the standard treatment for rectal adenocarcinoma. The tumour is resistant to radiation; doses above 80 Gy are necessary and have to be delivered by endocavitary irradiation. Contact radiotherapy is a basic method of delivering a high dose in a small volume. Brachytherapy can be used to deliver a boost of radiation into a residual lesion. External-beam radiotherapy can be used to supplement the dose to the deep part of the primary tumour and to the perirectal lymph nodes. T1N0 tumours have been treated by contact radiotherapy, and local control was achieved in 85–90% of patients with no severe toxic effects. Combined endocavitary irradiation and external-beam irradiation can achieve local control in 80% of patients with T2 tumours and 60% of patients with T3 tumours with only moderate toxic effects and a 60% 5-year overall survival. Radiotherapy alone is suitable for patients with T1N0 lesions (contact radiotherapy) or patients with T2–3 (combined endocavitary and external-beam radiotherapy) who cannot undergo surgery. For T2 or early T3 tumours of the lower rectum requiring surgery and a permanent colostomy, combined irradiation can be used as a first-line treatment in an attempt to avoid abdominoperineal amputation.