Isolated angiitis of the central nervous system is an uncommon clinicopathologic entity characterized by vasculitis restricted to the vessels of the central nervous system without other apparent systemic vasculitis. Experience with the diagnosis, treatment, and follow-up evaluation in four patients with this disease is presented. Early manifestations of disease include severe headaches, altered mental function, and focal neurologic deficits. The pattern of progression from headaches and altered mental status to multifocal neurologic deficits is particularly suggestive of the diagnosis of vasculitis of the central nervous system. Systemic symptoms such as fever, myalgia, arthralgia, and arthritis, which occur frequently in other vasculitic syndromes, are generally not present in patients with isolated angiitis of the central nervous system. No single laboratory study can firmly establish or completely exclude the diagnosis; consequently, tissue diagnosis with biopsy of the brain parenchyma and leptomeninges may be required. In two patients, recurrent disease developed despite treatment with corticosteroids alone. Sustained clinical remission was induced in all four patients with a regimen of daily cyclophosphamide and alternate-day prednisone therapy. Cyclophosphamide and alternate-day prednisone therapy are considered the treatment of choice in severe, progressive, or corticosteroid-resistant isolated angiitis of the central nervous system.