Postmortem quantification of the remaining optic nerve fibers in three eyes with nonarteritic anterior ischemic optic neuropathy showed that the loss of fibers was complete in the superior half of each nerve and included loss of peripheral fibers in the other half. The fibers with the greatest resistance to atrophy were found in the middle of the nerve cross section. The pattern was similar to that found in a previous example of anterior ischemic optic neuropathy and unlike that found in glaucoma or other optic neuropathies studied in similar fashion.