The precise etiology of transient neurologic deficits at high altitude is unclear, particularly since the subjects are not investigated as they would be had the events occurred in an urban environment. This report describes two subjects who experienced transient ischemic attacks (TIAs) while ascending the northeast ridge route of Mt. Everest during the Ultima Thule Everest Expedition, and a third subject with TIAs during three separate high-altitude climbs. Possible etiologies and treatment for TIAs at high altitude are suggested.