Lateral chest radiography in the investigation of thoracic lymphoma remains a feature of the current literature. This study assessed what information the lateral chest radiograph (CXR) adds in the follow-up of such patients. Eighty-eight patients with known lymphoma who had a CXR and thoracic CT within the same 4-week period were assessed. Five radiologists scored eight mediastinal and hilar nodal groups and eight extramediastinal regions on the frontal CXR as normal, equivocal or definitely abnormal (denoted 0, 1 and 2, respectively). This was repeated 1 week later with a combination of frontal and lateral films. Results were compared with the findings on CT which were scored similarly using accepted criteria for the presence of lymphadenopathy. Where the lateral CXR caused a change in score at any site, this change was compared with CT to determine the effect on diagnostic accuracy. For four of the five observers, the lateral film made no significant difference in diagnostic accuracy in the assessment of mediastinal lymph nodes. A fifth observer derived a small benefit from the addition of the lateral film, although almost 30 % of this was accounted for by changing from a wrong to an equivocal diagnosis. The lateral film did cause a small increase in the detection of pleuro-parenchymal lung lesions, although none of these were clinically significant. We conclude that routine lateral chest radiography is unhelpful in the follow-up of patients with lymphoma.