In immunocompetent children in Europe and the United States, varicella is usually a benign disease. However, infants born to women who acquire varicella during or shortly after pregnancy are at high risk of infection. For unknown reasons, the disease is more severe in adolescents and adults, with pneumonia the most common cause of death. Varicella may also be lethal in patients of any age in the presence of biologic or iatrogenic immunosuppression. It is now well documented that varicella-zoster virus remains latent in the dorsal root and cranial ganglia following an attack of varicella. Viral reactivation appears with advancing age as cellular immunity wanes. The contemporary relative aging of the population will enhance the social significance of zoster. The immigration of nonimmune adults in temperate climates poses a major problem in terms of protection of high-risk children. A vaccination program is indicated.