Varicella (chicken pox) is an acute, highly contagious viral disease with worldwide distribution, seasonal prevalence in winter and spring, characterized by generalized vesicular exanthema often accompanied by fever. While mostly a mild disorder in childhood, varicella tends to be more severe in adults and it may be fatal, especially in neonates and in immunocompromised subjects. Susceptible pregnant women can lead to severe, and even fatal, disease of the newborns. Following primary infection, the virus remains latent in neural ganglia, and upon subsequent reactivation VZV may cause zoster (shingles), a disease mainly affecting the elderly and immunocompromised persons, that consists in painful, circumscribed eruption of vesicular lesions with inflammation of associated dorsal root or cranial nerve sensory ganglia. IgM antibodies to varicella-zoster virus may be detected during primary and reactivated infection. Evaluation of specific immune status for VZV may guide management of immunosuppressed patients and administration of antiviral agents.