This chapter deals with isolated angiitis of the central nervous system (CNS), and begins with an overview of the pathology and pathogenesis of the condition. The nonspecific pathological pattern of isolated CNS angiitis is characterized by infiltrations of the vascular walls with mononuclear cells including lymphocytes, macrophages, and histiocytes. The pathogenesis of isolated CNS angiitis is unknown and progress is slow because of the rarity of tissue samples acquired from carefully documented cases. Brain imaging, angiography, and brain biopsy are the diagnostic options investigated in the chapter. In patients with a unique focal presentation such as stroke, and with isolated CNS angiitis suspected on the basis of angiography alone, a course of several-weeks of high-dose corticosteroids associated with a calcium channel blocker and no immunosuppressor can be proposed. The diagnosis of reversible cerebral angiopathy should be carefully considered in these patients.