PURPOSE: To evaluate the CT findings and incidence of complications occurring in intrathoracic extrapul-monary organs due to radiation therapy. MATERIALS AND METHODS: Among 82 patients who underwent chest CT before and after radiation therapy, 23, in whom the procedure provided no evidence of pericardial invasion or pleural effusion before radiation therapy, nor of significant improvement in the tumor after this therapy, were evaulated. Changes in the pericardium, pleura and mediastinal fat were retrospectively assessed. In comparing the CT findings obtained before radiation therapy with those obtained afterwards, changes in the pericardium and pleura were classified as effusion where low density fluid was present and as thickening where there was no fluid. If an increased abundance of soft tissue strands was seen within mediastinal fat, changes in this fat were deemed to have occurred. RESULTS: Among the 23 patients evaluated, changes in the pericardium [thickening (n=3 ; 13.0%) ; effusion (n=8 ; 34.8%)] were found in 11 patients (47.8%), and changes in the pleura [thickening (n=3 ; 13.1%); effusion (n=9 ; 39.1%)] in 12 (52.2%). In no patient with pericardial or pleural effusion was thickening or contrast enhancement of the pericardium or pleura evident. In seven cases(30.4%), soft tissue strands within mediastinal fat had become more abundant. CONCLUSION: The CT findings which demonstrated complications resulting from radiation therapy were pericardial or pleural thickening or effusion and an increased abundance of soft tissue strands within mediastinal fat. In contrast to previous reports, pericardial and pleural change after radiation therapy was a common finding in our study, occurring in 69.6% of cases.