Eighteen patients with mediastinal Hodgkin's disease treated with chemotherapy first, then irradiation were investigated during 1 year by means of 5 CT and radiological examinations of the chest. Four months after irradiation pericardial thickening was detected in 60 p. cent of the patients. The authors underline the high frequency, early occurrence and usually spontaneous resolution of radiation-related pericarditis without clinical or radiological signs.