Stroke is uncommon in HIV-positive individuals. There is mounting evidence to indicate that HIV infection is associated with an increased risk for both ischemic and hemorrhagic stroke. A number of mechanisms, discussed in this chapter, have been proposed for this increased risk including prothrombotic states, other secondary causes such as cerebral infections and cardioembolic causes, as well as a primary HIV associated vasculopathy. The most common mechanisms cited for stroke development in AIDS patients are: (1) hypercoagulable or prothrombotic states; (2) other secondary causes such as brain embolism and cerebral infections; and (3) direct primary HIV-associated vasculopathies. Two forms of vasculopathy have been described that have been considered to be HIV-specific: small vessel HIV-associated vasculopathy which is an asymptomatic vasculopathy, and large- and medium-vessel HIV-associated vasculopathy which involves both extracranial arteries as well as medium-sized intracranial vessels.