The chest radiographs (CXRs) of 110 patients with mediastinal Hodgkin's disease (HD) were reviewed to determine the incidence, degree, and significance of mediastinal abnormalities following treatment. Residual mediastinal abnormalities were defined as either minimal or measurable, and occurred in 64% of all patients at the completion of treatment, but were more common in those with bulky mediastinal disease at presentation (40 of 48, 83%). Fifty-one patients with a mediastinal abnormality at the end of treatment had follow-up films available. Partial or complete regression of the abnormality occurred by 1 year in 30 of these patients (59%). Over a median follow-up of 80.5 months, there were more relapses (13 of 70, 19%) in patients with residual abnormalities following treatment than in those where the mediastinum was considered normal (four of 40, 10%). Measurable abnormality was associated with a higher relapse rate (six of 25, 24%) than minimal abnormality (seven of 45, 16%), but none of these differences were statistically significant. the subsequent relapse rate for patients with persisting abnormality at 1 year was 14%, compared with 17% for patients in whom regression had occurred and 14% in whom the mediastinum had always been considered normal. Considering the whole group, the presence of a mediastinal abnormality following treatment did not predict for relapse, but for the 34 patients treated by chemotherapy (CTR) alone, a residual abnormality was associated with a significantly higher relapse rate (P = .029). We conclude that following mediastinal radiotherapy (XRT) administered either alone or combined with CTR, residual mediastinal abnormalities do not indicate the need for further treatment. However, following CTR alone, such abnormalities may signify persisting disease and we recommend that XRT be considered for these patients.