Three new human herpesviruses (HHVs) have been discovered over the last 14 years. Two of these, HHV-6 and HHV-7, are widespread with infection usually acquired in early childhood. The third, HHV-8, is less prevalent and is etiologically associated with the malignancies Kaposi’s sarcoma (KS), multicentric Castleman’s disease, and primary effusion lymphoma. As with other herpesviruses, each has the potential to be pathogenic in the post-transplant period. HHV-6 has been associated with a range of clinical disease in solid organ and bone marrow transplant recipients, including encephalitis, bone marrow suppression, and graft rejection. HHV-7 has been associated with an increased risk of cytomegalovirus disease following renal transplantation. Although HHV-8 is relatively uncommon in transplant recipients, iatrogenic immunosuppression increases the incidence of KS, particularly following renal transplantation. Reactivation can occur in persons with prior infection or HHV-8 may potentially be acquired through the donor allograft. Other risk factors for transplant-associated KS include ethnic origin, and the type and degree of therapy-induced immunosuppression.