A 43-year-old woman presented with painful visual loss and optic disk edema in the right eye (OD) diagnosed as optic neuritis. Initial non-gadolinium-enhanced fat suppressed cranial magnetic resonance imaging (MRI) was normal. Three months later, the disk edema persisted and a gadolinium-enhanced MRI scan of the brain and orbits with fat suppression showed enhancement of the optic nerve OD, most consistent with an optic nerve sheath meningioma. The diagnostic difference between optic neuritis and optic nerve sheath meningioma is discussed. © 2001 by Elsevier Science Inc. All rights reserved.