A 56-year-old diabetic man underwent heart transplantation for end-stage ischemic heart disease; fever, progressive thrombocytopenia, and hepatitis developed 8 weeks after transplantation. Cytomegalovirus was cultured from the serum buffy coat. In spite of therapy with high-dose ganciclovir sodium, the patient died on the seventy-seventh postoperative day. Autopsy revealed a previously unsuspected high-grade B-cell lymphoma with extensive hepatic replacement.