Central nervous system (CNS) infections range from rapidly fatal bacterial meningitis to slowly progressive infectious processes from mycobacterial, fungal, or viral agents. The diagnosis of acute bacterial meningitis is made by the examination of cerebrospinal fluid (CSF). Brain abscess is a suppurative infection involving brain parenchyma. Although the CNS infections most commonly associated with HIV infection are toxoplasmosis and cytomegalovirus (CMV), such patients are susceptible to many other infections including aseptic meningitis, neurosyphilis, and M. tuberculosis. The term aseptic meningitis has been used to describe conditions of acute meningeal irritation that prove to be benign and self-limiting. The incidence of tuberculosis (TB) is on the rise, due to an increase in numbers of HIV-infected persons, numbers of homeless individuals, and immigrants from developing countries. Cryptococcus neoformans, a common fungal pathogen, commonly affects HIV infected patients. Viral encephalitis is an infectious and inflammatory process involving the brain.