There is both clinical and histopathologic evidence for peripheral visual field loss and optic nerve degeneration in longstanding papilledema due to idiopathic intracranial hypertension (IIH). The purpose of this study was to look at the extent and distribution of axonal dropout in secondary optic atrophy due to IIH. Both optic nerves from a 29-year-old man with a two year history of IIH were examined histologically and morphometrically. A high-contrast lipid (myelin) stain, paraphenylenediamine (PPD), and a semiautomated image analysis system were employed to resolve sufficiently the optic nerve fiber images for counts and for measurement. There were 80% and 90% losses of axons, respectively, in the right and left optic nerves consequent to IIH. The axonal loss in the peripheral area of each optic nerve was much more severe than that in inner sectors (= 0.001 for the right optic nerve and = 0.005 for the left). This pattern of axonal dropout is consistent with the preservation of good central visual acuity despite devastating optic nerve atrophy, and with the severe peripheral visual field loss noted in this patient.