I compared six subjects with pseudotumor cerebri and unilateral or highly asymmetric papilledema with 20 such patients with bilateral papilledema. Patients with unilateral papilledema were significantly older than those with bilateral papilledema, but there were no significant differences between the two groups in disease duration, elevation of intracranial pressure, visual fields and acuity, and presence of headaches or transient visual obscurations. I hypothesize that, in patients with unilateral papilledema, one optic nerve is protected from pressure effects by optic nerve sheath anomalies or lamina cribrosa changes due to increased collagen and decreased elasticity with aging.