Neurologic dysfunction complicating HIV infection may occur in up to 70% of AIDS patients. The advent of highly active antiretroviral therapy has reduced central nervous system opportunistic infections. Immune reconstitutions after highly active antiretroviral therapy also lead to atypical presentations of neurologic opportunistic infections. We report a man who developed an encephalitic illness 10 months after institution of highly active antiretroviral therapy and improvement in his CD4 count. Varicella zoster vasculitis involving the brain was suspected. Acyclovir therapy resulted in complete clinical and radiologic recovery. Symptomatic reactivation of varicella zoster infection within the encephalon during therapeutic immunologic reconstitution is rare and should be suspected, especially in patients with neurologic syndrome consistent with encephalitis with recent history of herpes zoster and multiple, discrete areas of infarct or demyelination on brain magnetic resonance imaging. The clinical and neuroradiologic features of this condition and its relevance to the immune reconstitution syndrome are discussed.