Adolescents and adults have an increased risk of severe and, rarely, fatal varicella. Increased risk of exposure of susceptible teens and adults occurs because of the more common use of day care and nursery programs, and more common exposure of health care workers to herpes zoster. The exposure of susceptible parents to their own children represents an important hazard. Live attenuated varicella vaccine requires two doses to be adequately immunogenic in adults. Safety and clinical tolerability have been well documented, and persistent antibody protection from infection and virtual absence of early herpes zoster infections are inferred from encouraging preliminary data.