Herpes simplex virus infections in immunocompromised individuals have clinical features that are often quite different from primary and secondary HSV infections in otherwise healthy people. These infections should be recognized early and treated promptly to prevent progression of the lesions and the possible systemic dissemination of the virus. Cytological and biopsy examination frequently discloses changes characteristic of HSV-1, HSV-2, or Varicella-zoster virus. To ensure the most precise diagnosis, however, these examinations should be complemented by viral isolation and serological studies.