Interferon alpha is a biologic agent with demonstrated anti-tumor activity in a variety of hematologic and solid malignancies. Many patients treated with interferon experience acute toxicity manifested as a flu-like syndrome of fever, chills, myalgias, and malaise. However, fatigue, anorexia, bone marrow suppression, nausea, vomiting, dizziness, and confusion may also occur. Cardiotoxicity is a rare complication of interferon therapy that most frequently presents as transient episodes of hypotension and tachycardia, with few significant life-threatening cardiovascular effects reported. A small number of cases of suspected interferon-induced cardiomyopathy, all of which improved after discontinuing interferon, have recently been documented. We report a patient with multiple myeloma who developed severe congestive cardiomyopathy while receiving interferon alpha that did not reverse subsequent to discontinuation of interferon therapy. Although the patient had previously received doxorubicin, the presence on endomyocardial biopsy of a prominent intracellular lipid accumulation within myocytes and only grade 2 anthracycline cardiotoxicity suggested that other or additional factor(s) contributed to the severity of this patient's cardiomyopathy. Etiologies of cardiac dysfunction other than interferon and doxorubicin were excluded. While a direct cause-effect relationship between interferon alpha and irreversible congestive cardiomyopathy cannot be firmly established in this case report, patients who either concurrently or sequentially receive interferon and anthracyclines should be carefully monitored for evidence of cardiac toxicity.