Randomised trials in which the omission of radiotherapy has been tested after breast-conserving surgery, with or without adjuvant systemic therapy, show a significant four- to five-fold reduction in local recurrence. As yet, no subgroup of women managed by breast-conserving surgery has been identified from whom radiotherapy can be withheld. Few randomised data have been published on the effect of omission of radiotherapy on local control, quality of life and costs, particularly in older women for whom the risk of local recurrence is generally lower. Ongoing trials are evaluating the role of radiotherapy in this population of low risk, older women. Adjuvant radiotherapy after breast-conserving surgery or mastectomy significantly reduces the incidence of local recurrence. In women who have had a mastectomy at high risk of recurrence (> 20% risk of recurrence at 10 years), adjuvant radiotherapy improves survival if combined with adjuvant systemic therapy. Among women with T3 tumours, and those with four or more involved axillary nodes treated by mastectomy, postoperative radiotherapy is the standard of care. For women at intermediate risk of recurrence (i.e. <15% 10-year risk of recurrence after surgery and systemic therapy alone), with one to three involved nodes or node negative with other risk factors, the role of radiotherapy is unclear. Clinical trials to assess the role of postmastectomy radiotherapy (PMRT) in this setting are needed. For pT1-2, pNO tumours without other risk factors, there is no evidence at present that PMRT is needed.