We describe two cases of severe constrictive pericarditis arising after allogeneic BMT conditioning involving total body irradiation and melphalan to treat Philadelphia-chromosome positive ALL. Both patients required pericardectomy, resulting in marked improvement in ventricular filling. However, a degree of right-sided cardiac failure persisted in both patients secondary to restrictive cardiomyopathy. Constrictive pericarditis has not been previously described after BMT, but has been observed following thoracic radiotherapy for malignancy, usually involving a substantially higher radiation dose. Pericardial constriction and restrictive cardiomyopathy should be considered as causes of breathlessness and/or oedema occurring late after BMT. Bone Marrow Transplantation (2000) 25, 571-573.