The principal aim of this chapter is to provide an illustrated review of the neuropathologic features of common and recently emerging central nervous system (CNS) viral diseases. An overview of the histopathologic features common to most viral infections of the central nervous system will be provided. This will be followed by a description of the gross and microscopic findings characteristic of specific viral infections of the CNS. Conditions which can be accurately diagnosed via brain biopsy and their differential diagnosis will be emphasized. Where appropriate, ancillary studies including molecular diagnostic techniques will be covered.