Vasculitis of the central nervous system can be of several varieties depending upon the vessel(s) involved and type of disorder. One can see primary CNS vasculitis as a distinct entity which is primarily manifested as central nervous system injury in a vascular distribution or the vasculitic process can be secondary to a systemic disorder such as systemic lupus erythematosus (SLE) or polyarteritis nodosa (PAN). The inflammation of the CNS vessels can be immune mediated or infectious in nature and a number of "triggers" have been identified including hypersensitivity states. It is quite probable that there is a genetic predisposition in certain individuals and this can lead to an enhanced risk of a vasculitic process when there is exposure to a particular antigen that "sets off" the immune system. The potential for response of the process to antimicrobials and/or immunosuppressants, and the potential for devastating consequences if the process is left untreated, has heightened the urgency in recognizing CNS vasculitis. Key to the recognition and treatment of CNS vasculitis is the evolution of newer insights into the pathogenesis. For example, it is evident that most vasculitides are cell-mediated. Antigen stimulation of CD4+T cells is believed to play a crucial role in giant cell (temporal) arteritis which is the most common type of CNS vasculitis. Identification of genetic susceptibility has also contributed to our understanding of the cascade of events that leads to vascular injury on an inflammatory basis.