In order to assess the importance of personality and expectations in the development of Acute Mountain Sickness (AMS), 3 standard personality questionnaires and a Mountain Sickness Anticipation Questionnaire were completed by all of the 17 BMRES expedition members before their departure for the Himalayas. AMS could not be predicted with these tests and its occurrence, when assessed either by clinical interview or by peer review, bore no significant relationship to personality. For comparison daily self-assessment of the signs and symptoms of AMS were also conducted throughout the expedition, using graduated and graphic rating scales. The results were found to be unreliable and dependent upon personality factors. These findings have implications for those assessing others at high altitude.