Background Acute mountain sickness (AMS) affects almost half of those ascending to heights over 3,000 m. The knowledge and practices concerning AMS have not been adequately studied.

Methods We conducted a prospective on-site study in the Himalayas. Between July and October 2004, we approached a convenience sample of trekkers during or after their ascent to high altitudes and provided them with detailed questionnaires regarding knowledge of and personal experience with AMS.

Results One hundred ninety-two travelers (of whom 106 were Israelis and 86 Western Europeans) participated in the study. One hundred thirty travelers (68%) had received any written/oral information about AMS prior to their departure. The most common source of information among Israeli travelers was the travel clinic (65%), compared to only 9% among Europeans. Overall, 89% were found to have good “basic knowledge” about symptoms of AMS (defined as headache plus ≥2 of the following: fatigue, dizziness, nausea, insomnia). Travelers who had received information about AMS prior to their trip were significantly more knowledgeable about symptoms of AMS (p= 0.0001), and treatment options, such as oxygen, medications, and rest (p= 0.023, p= 0.024, p= 0.011, respectively). Only 2% of the Israelis versus 16% of the Europeans (p= 0.0004) knew that O2 was a treatment option. Forty-seven percent suffered from AMS, which in 50% began at 3,000 m. About 33 of 90 (37%) of those who suffered AMS symptoms had acetazolamide with them, but only 14 actually used it as treatment.

Conclusions Knowledge of AMS among climbers to high altitudes should be fostered, with specific emphasis on practical advice.