Several factors, including T stage, nodal involvement, grade, the presence of lymphovascular invasion, and possibly involved or close surgical margins, have been found to affect local recurrence after mastectomy. The majority of recurrences will occur in the first 5 years and 50% of patients will have metastatic disease at the time of recurrence. Early studies on the use of adjuvant radiotherapy are difficult to interpret owing to poor radiotherapy techniques, inadequate dose or a variety of confounding variables within a particular trial. More recent reports have confirmed that adjuvant radiotherapy will reduce the risk of local recurrence and in tumours of <5 cm with involved nodes, produce a reduction in breast cancer deaths. Improvements in breast cancer mortality may however be counterbalanced by increases in cardiac events and deaths caused by second malignancies. This stresses the importance of using megavoltage irradiation and avoiding excess cardiac doses particularly when treating left-sided tumours. Adjuvant radiotherapy combined with tamoxifen has been shown to produce an improvement in both local control and survival in postmenopausal node-positive patients who have undergone mastectomy. Adjuvant radiation combined with systemic chemotherapy has a significant effect on local recurrence and probably on survival in node-positive patients after mastectomy. There is little controversy over its role in patients with tumours >5 cm, with more than four nodes involved or with one to three nodes with extracapsular extension, or in those in whom axillary surgery has been deemed inadequate (i.e. <10 nodes). Debate still exists concerning T1/T2, G1/G2 tumours with only one to three nodes involved when the axillary surgery has been satisfactory (>10 nodes). The ongoing Intergroup trial may answer this question but until then other factors such as tumour grade and the presence of lymphovascular invasion can be included in the equation to determine which of the patients in the latter group should receive postoperative radiotherapy. Controversy still exists about what fields should be irradiated and in particular whether the supraclavicular fossa and internal mammary node chain should be included in adjuvant therapy. The EORTC is presently conducting a randomized trial, which should give us the answer. Treatment at relapse on the chest wall may require a combination of surgery, radiotherapy and chemotherapy, depending on previous therapy. If radiotherapy has not previously been used, then wide-field irradiation should be administered, including both chest wall and supraclavicular fossa with or without the axilla, depending on the extent of previous axillary surgery and the risk of lymphoedema. Re-irradiation after radical adjuvant radiotherapy can be considered only for selected patients when an adequate discussion with them has taken place with regard to the relative benefits versus toxicity.