Herpesvirus infections of the CNS are prevalent in all segments of the population, and are an important health care issue. The family of herpesviruses consists of a large group of double-stranded DNA viruses that includes herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2 (HSV-2), cytomegalovirus, Epstein-Barr virus, varicella-zoster virus, B virus, herpesvirus 6, and herpesvirus 7. In addition to producing infection when the host initially acquires the virus, an important property shared by these viruses is the ability to produce latent infection and to be reactivated.