Herpesvirus infections are a major cause of morbidity and mortality in immunosuppressed patients. Bone marrow and organ transplant recipients are model patient populations for studying the natural history of herpesvirus infections because the infections occur predictably after transplantation. Herpes simplex virus infections occur within the first month after transplantation and may cause severe mucocutaneous disease. Cytomegalovirus infections occur one to three months after transplantation and are the major viral cause of morbidity and mortality. Varicella-zoster virus infections occur four to five months after transplantation and rarely cause life-threatening infection. Further studies of Epstein-Barr virus are necessary to determine its significance as a pathogen. The development of new antiviral agents has introduced effective therapeutic approaches for herpes simplex virus infections and varicella-zoster virus infections. Efforts to treat or prevent cytomegalovirus infections in transplant recipients have had limited success. However, new therapeutic strategies may lead to therapies which may reduce the severity of these infections and lead to increased survival in bone marrow transplant and organ transplant recipients.