Delayed chronic constrictive pericarditis developed in seven patients 51 to 268 (mean 116) months after radiotherapy. Six of the seven complained of exertional dyspnea that was initially believed to be caused by mediastinal fibrosis. All patients had raised jugular venous pressure, although in two patients this finding was not appreciated by the primary physician. There were no consistent noninvasively identifiable features to allow prediction of constrictive pericarditis other than consideration of its existence and careful examination of the cardiovascular system. All patients had constrictive pericarditis proved at cardiac catheterization. Of the five patients who underwent pericardiectomy, two had an excellent functional result, one has residual pericardial constriction and two died of unrelated causes. Recommendations for the treatment of radiation-induced pericardial disease are given.