Idiopathic intracranial hypertension (pseudotumor cerebri) produces loss of visual field and visual acuity. We conducted a retrospective study of 12 patients (all female, ranging in age from 6 to 44 years) using computerized visual field analysis. In seven of the 12 patients, the visual field loss appeared to be permanent, and follow-up was too short for the final outcome to be determined in two others. The visual field defects were those known to be associated with optic disk lesions. The most common were blind spot enlargement (all 12 cases), isopter constriction (nine cases), and loss on the nasal side of the visual field (seven cases), especially in the inferonasal quadrant. Four patients had diminished visual acuities. The reversibility of the visual field defects was correlated with the presence (nonreversible) or absence (reversible) of ophthalmoscopic signs of chronic papilledema. Because visual loss is reversible if treatment is begun before the onset of the optic disk changes associated with chronic papilledema, patients with idiopathic intracranial hypertension should be monitored carefully with frequent perimetric and visual acuity testing.