Developments in the evaluation and systemic management of diffuse large B-cell lymphoma (DLBCL) require ongoing assessment of the role of external beam radiotherapy in management. This review assesses data regarding the use of radiotherapy in the initial management of early stage and advanced DLBCL, and considers the implications of bulky and residual disease, and the contribution of PET scanning, to decisions regarding the use of radiotherapy after chemotherapy. Limited R-CHOP plus radiotherapy, or full dose R-CHOP alone, are both likely to cure approximately 90% of patients with low risk early stage disease. The choice of therapy will depend on considerations of acute and late toxicity of the two approaches, taking into account individual patient risk profiles and preferences. Unfavorable early-stage and advanced-stage disease require treatment with full dose R-CHOP. The presence of bulky disease predicts for a higher risk of relapse, which may be partly ameliorated by the addition of radiotherapy. The rapidity of response on PET scanning, the presence of a posttherapy residual mass, the potential toxicity of radiotherapy and the available salvage options all need to be considered on a patient by patient basis, when considering the use of radiotherapy for advanced disease.