A 35-year-old man on a trek to the Mount Everest region of Nepal presented with a sudden, acute confusional state at an altitude of about 5000 m. Although described at higher altitudes, delirium presenting alone has not been documented at 5000 m or at lower high altitudes. The differential diagnosis which includes acute mountain sickness and high altitude cerebral edema is discussed. Finally, the importance of travelling with a reliable partner and using proper insurance is emphasized in treks to the Himalayas.