The authors report a case of acute mountain sickness (AMS) experienced by a support member of the Ultima Thule Everest Expedition. The subject arrived at the 17,000-ft base camp by truck and then developed the symptoms of AMS over the following 72 hours. Flash-induced visual evoked responses (VERs), tetrapolar impedance pulmonary plethysmography, and oxygen saturation measurements were performed. These changed from normal before the onset of his symptoms to abnormal during the height of the symptoms and reverted to normal after treatment. This is the first reported case of AMS monitored with VERs. It has been postulated that AMS may be an early form of cerebral edema, and this report corroborates this hypothesis.