Objective.—To determine the burden of and risk factors for diarrheal illness among mountaineers climbing Denali during the spring of 2002.

Methods.—We conducted a retrospective cohort study of all willing and available climbers who returned to base camp from June 11 to 14, 2002. We used a questionnaire that addressed illness status, demographics, and potential risk factors for illness. A case of diarrhea was defined as self-reported diarrhea (loose stool) in a Denali climber who did not have diarrhea before arrival at base camp.

Results.—Thirty-eight (29%) of the 132 climbers who were interviewed reported experiencing diarrhea at some point on the mountain. Spending 8 or more days at the 17 200-foot high camp; being a member of a climbing party in which at least 1 other person also had diarrhea, especially if tent occupancy was 3 or more; and not receiving education about disease risk-reduction techniques among climbers who were on a guided expedition were associated with increased risk of illness.

Conclusions.—To prevent infectious diarrheal outbreaks among mountaineers climbing Denali (and other highly trafficked alpine routes), we recommend that park staff provide climbers with detailed information related to minimizing disease risk and develop more effective strategies for preventing climbers from depositing fecal material directly into snow along the route, such as establishing and enforcing firmer penalties for noncompliance with existing human waste disposal regulations and requiring the use of personal stool-hauling devices.