A 71-year-old man had a 3-year history of a recurrent seronegative autoimmune constrictive pericarditis and pleural effusions, which were treated with pericardiectomy and prednisone and azathioprine. The pleural fluid was transudative and sterile, and the pericardium contained focal lymphoplasmacytic aggregates. Attempts to taper immunosuppressive drugs failed because of a recrudescence of the inflammatory syndrome and pericardial effusion. The patient was admitted with fever of unknown origin with a surge of the inflammatory syndrome and pancytopenia. He reported night sweats beginning 3 weeks prior associated with fever and unintentional weight loss. No lymphadenopathy was noted.