Objective: The number of lowland dwellers traveling at high altitudes has greatly increased in recent decades. Business travelers flying to La Paz or Lhasa are at risk of altitude illnesses, similarly to miners and soldiers transported to high altitudes. Traveling to high altitude requires adaptation and if this process fails due to too rapid an ascent rate or susceptibility of the climber, acute mountain sickness (AMS) may result. Doctors and nurses in travel clinics, health centers and occupational health care clinics may face patients asking advice on how to plan their trips or manage AMS, or the health care personnel may take part in a travel to high altitude environment. Methods: Two patients, aged 29 and 47 years, who fulfilled the criteria for AMS were studied. The clinical findings and treatment in the field are described including the review of the current recommendations for prevention and treatment of AMS. Results: Both patients developed a severe AMS due to too rapid ascent and their denial of the symptoms. Conclusions: Prevention is the safest and the most efficient method in the care concerning AMS. Realizing the risk of mountain sickness, active inquiry about the symptoms and correctly timed reaction to them, in other words interrupting the ascent or descending, help to reduce and even to prevent the development of serious problems.