Herpes zoster infections (localized and disseminated) are more frequent and severe in immunosuppressed patients. Dissemination of virus may occur to skin and to viscera but is associated primarily with increased morbidity rather than mortality. Involvement of the central nervous system can occur with localized or disseminated infection, including 2 clinically distinct forms of encephalitis. Studies of the pathogenesis of infections are hampered by the absence of a convenient animal model. However, circulating antibody to varicella-zoster virus can be measured with recently devised, sensitive serologic techniques. Controlled studies of adenine arabinoside in the treatment of herpes zoster in immunosuppressed patients have yielded promising results. Antiviral chemotherapy may represent a significant control measure for these infections in the future.