A 26-year-old woman who had undergone orthotopic heart transplantation because of dilative cardiomyopathy received a triple-drug immunosuppressive regimen (cyclosporine A, azathioprine, and prednisolone). During her relatively frequent episodes of acute rejection, she was treated with methylprednisolone and repeated application of ATG. A short time before the patient's death, a fine-needle aspiration of the liver revealed the cytologic diagnosis of a malignant pleomorphic medium-size cell non-Hodgkin's lymphoma of a higher grade of malignancy. Immunosuppression was reduced, and the patient died in cardiogenic shock related to a histologically confirmed episode of severe acute rejection 264 days after the transplantation. On autopsy, the malignant lymphoma previously diagnosed by fine-needle aspiration cytology was found to be present in the liver as the only extranodal localization. The immunohistologic analysis of the immunophenotype specified the lymphomatous neoplasia as a T-cell lymphoma. The particular importance of this case is that it is, to our knowledge, the third case of proven T-cell lymphoma following organ grafting documented in the literature and the first case described in a cardiac allograft recipient.