This chapter deals exclusively with varicella-zoster virus (VZV) pneumonitis — its pathogenesis, clinical manifestations, diagnosis, management, and prognosis. VZV produces two distinct clinical syndromes: varicella in children and herpes zoster in adults. The diffuse papulovesicular rash characteristic of varicella appears in crops over a 3- to 5-day period and is the initial manifestation of VZV infection. The diagnosis of VZV pneumonitis is based upon typical radiographic findings of bilateral, ill-defined nodular infiltrates in the presence of the cutaneous rash. Herpes virus particles, apparent from electron microscopic examination of negatively stained vesicle fluid or multinucleated giant cells with intranuclear inclusions evident from a Tzanck test of a fresh vesicle, provide support for a VZV origin of the cutaneous lesions. Two drugs, acyclovir and adenine arabinoside, are effective in the treatment of VZV infections. The role of corticosteroids in the treatment of severe VZV pneumonitis remains controversial.