Objectives.—To describe physiological attributes (height, weight, sex, resting heart rate, etc) of climbers attempting to summit Mt Everest and to investigate differences between successful and unsuccessful summiteers.

Methods.—One-hundred thirteen Everest climbers were surveyed by questionnaire before and after the spring 2003 climbing season. Climbers' previous high-altitude climbing experience and physical characteristics were recorded, as well as health before and during expedition, medication used, body weight before expedition and after summit attempt, and ultimate summit success or failure.

Results.—The most common afflictions among climbers were cough, diarrhea, nausea, and vomiting, and the most common medications used were acetazolamide, aspirin, and antibiotics. Average postacclimatization, presummit “rest” altitude was 4571 m, and average weight carried 10.7 kg. Average body mass loss during expedition, regardless of success, was 7%.

Conclusions.—Oxygen use and existence of gastrointestinal disorders are strongly correlated with success in summiting Mt Everest. On the other hand, a history of acute mountain sickness before the attempt is correlated with failure in summiting Mt Everest. Several other factors were found to be marginally correlated with chance of success, but the power of the study was limited by a low postsummit attempt questionnaire return rate (34%).