Infections by VZV, the virus that causes chickenpox and herpes zoster, usually are diagnosed by the classic clinical presentations. In immunocompromised patients, however, the atypical presentation can make the diagnosis more challenging. Although varicella typically follows an uncomplicated course in children, adults and immunocompromised patients can develop complications involving several organs; some complications may be fatal. Prevention of disease with the vaccine is ideal. When varicella or zoster infection does occur, proper treatment should be initiated, depending on the age and immune status of the patient.