1. Altitudes of 8,000 to 14,000 feet (2438 to 4267 meters) are attained regularly by skiers, hikers, and climbers in the continental United States. Outside the US, mountain climbers may reach altitudes of up to 29,035 ft (8848 m) (Mount Everest).
2. Most difficulties at high altitude are a direct result of the lowered concentration of oxygen in the atmosphere. At 18,000 feet (5487 m) there is half the oxygen that is available at sea level. A person transported suddenly to this altitude without time to acclimatize or without the provision of supplemental oxygen would probably lose consciousness.

Acclimatization requires gradual exposure to altitude, with a rate of ascent not to exceed 1,500 feet (457 m) per day at altitudes above 8,000 feet (2438 m). Rest days at a constant altitude are essential at heights above 10,000 feet (3048 m). Acclimatization is achieved by adhering to a schedule of ascent:

1. For any climb above 8,000 feet (2438 m): Spend an initial 2 to 4 days at 5,000 to 7,000 feet (1524 to 2134 m). The first day should be a rest day. If any person shows signs of altitude-related illness, spend additional time at that altitude.
2. For any climb above 13,000 feet (3962 m): Add 2 to 4 days for acclimatization at 10,000 to 12,000 feet (3048 to 3658 m). Subsequent climbing should not exceed 1,500 feet (457 m) per day. Scattered rest days are advised, along with an extra night for acclimatization with any ascent of 2,000 feet (609 m) or more. Sleep at the lowest altitude that does not interfere with the purpose of the expedition.
3. The drug acetazolamide (Diamox) has proven to be useful in stimulating breathing, diminishing the sleep disorder associated with AMS, facilitating the body's normal adjustment to high altitude, and improving nocturnal oxygenation.
   • Acetazolamide should be used if an ascent will be unavoidably rapid.
   • Children who have previously suffered from acute mountain sickness may benefit from acetazolamide.
   • Diamox is no substitute for proper acclimatization!
4. Avoid the use of alcohol, stay warm, keep out of the wind, avoid exhaustion, and eat regularly to avoid weight loss. A diet relatively high in carbohydrates is preferable to one high in fat and protein.