Twenty-three patients with chronic papilledema associated with pseudotumor cerebri underwent "modified" optic nerve sheath decompression for treatment of visual acuity and visual field loss. Instead of removing a single, rectangular section of optic nerve meninges, the operation was modified by making at least three longitudinal incisions in the sheath and then lysing arachnoid adhesions with a tenotomy hook. Twenty-one of the 23 patients demonstrated improved visual function after the initial surgery for a mean (+/- SD) follow-up of 21.5 +/- 12.3 months (median, 25 months; range, three to 45 months) without reoperation or reinstitution or oral corticosteroid and diuretic therapies. The two patients failing to improve after the first surgical procedure initially had a single meningeal window created and subsequently improved following reoperation with the modified procedure. Twelve of 21 patients with bilateral visual loss had improved visual function bilaterally after unilateral surgery. Six of the 21 patients needed bilateral surgery, and the other three had minor visual field defects in the second eye not severe enough to warrant surgery. Preoperative optic disc pallor did not predict a poor postoperative result. Optic nerve surgery improved the visual function in six patients who had failed to recover vision after one or more lumbar-peritoneal shunts.