A 38-year-old woman developed incoherent mentation, tremor, ataxia, and bilateral optic disc edema with mildly depressed visual acuity, nerve fiber bundle defects, and a left afferent pupillary defect. Magnetic resonance imaging of the brain disclosed striking linear contrast enhancement radiating from the ventricular borders. Lumbar puncture showed a normal opening pressure with a lymphocytic pleocytosis and elevated protein. On the basis of these findings, the initial diagnosis was viral or post-viral meningoencephalitis and the patient was not treated. During the next 4 weeks, her condition worsened. A brain and meningeal biopsy disclosed findings typical of primary angiitis of the central nervous system. With aggressive treatment, her neurologic status and magnetic resonance imaging normalized and her optic neuropathy improved markedly. Optic neuropathy and linear magnetic resonance imaging enhancement should be recognized as features of primary angiitis of the central nervous system.