A 30-year-old man with mild exertional dyspnea of recent (2 months) onset was found to have a massive pericardial effusion. The patient had received mediastinal irradiation for Hodgkin’s disease over 9 years previously. No evidence of recurrent lymphoma or other causes of pericarditis could be found. Following subtotal pericardiectomy, the patient developed a syndrome characterized by precordial discomfort, low-grade fever, tachycardia, and friction rubs. The electrocardiogram, normal preoperatively, showed diffusely negative T waves. Antimyocardial antibodies appeared in the serum. The syndrome, a hitherto unrecognized sequela of pericardiectomy, is interpreted as a mediastinoepicarditis, of possibly autoimmune origin.