The chest radiograms (CXR) of 102 patients with Hodgkin's disease presenting with mediastinal involvement at diagnosis were reviewed to assess the incidence and relevance of residual mediastinal abnormalities after therapy. All patients had completed planned treatment and had no evidence of persisting extramediastinum disease at restaging. Thirty-nine cases (38 per cent) showed residual mediastinal widening at the end of therapy (minimal changes in nine and measurable changes in 30 cases). Neither presenting features nor treatment modality correlated with residual mediastinal mass on chest X-ray. The isolated intrathoracic relapse rate was 11 per cent for patients with normal mediastinum following therapy, as compared with 20.5 per cent for those with residual widening; this difference did not reach statistical significance (p = 0.3). The persistence of mediastinal abnormalities was associated with a trend towards a higher risk of intrathoracic relapse for patients with initial bulky disease (p less than 0.05) and for those with B symptoms (p = 0.07). Using thoracic CT scan for restaging (56 patients), the residual mediastinum rate rose to 70 per cent; the predictability of local relapse with this procedure was not greater than with conventional X-ray study.