Optic nerve sheath decompression surgery improved visual function for 12 of 14 patients with progressive nonarteritic ischemic optic neuropathy (NAION). Visual recovery was maintained in all patients during a follow-up period of 6 to 18 months (average, 11 months). Seven patients had experienced a previous NAION in the eye that was not operated on that did not improve spontaneously. Surprisingly, 2 of these 7 eyes with long-standing decreased vision demonstrated some visual improvement after surgery on the contralateral, acutely affected eye. Spontaneous visual improvement did not occur in an age- and sex-matched control group of 12 patients with similar entry-level visual acuity and field loss. Only 1 of 3 patients with sudden, nonprogressive visual loss secondary to NAION improved after surgery. In a control group with nonprogressive NAION, 2 of 15 eyes (14 patients) demonstrated spontaneous improvement. Optic nerve sheath decompression improves visual loss due to progressive NAION, a disorder without any previously effective therapy. However, for acute, nonprogressive NAION, surgery for a small number of patients did not improve the natural history of the disease.