This investigation explores the relationship between psychological factors and acute mountain sickness (AMS). AMS occurs in most people staying more than a few hours above 3500 m. Symptoms include headache, nausea, vomiting, insomnia, anorexia, etc. Subjects studied were climbers preparing for an expedition to the Himalayas (80 men and 20 women). The psychological investigation consisted in two mono-factorial tests: STAI (anxiety inventory) and Bortner stress scale. After the expedition, subjects were classified into two groups: those who were susceptible to AMS and those who were not. Results indicated that the two groups differed for trait-anxiety on one hand, and for the level of anxiety before the final ascent on the other hand. In both cases, subjects susceptible to AMS were significantly more anxious than those who were not.