Altitude sickness if a serious consideration if you are climbing or trekking in Nepal and it's essential that you investigate the causes, symptoms and treatment of altitude sickness before you travel to Nepal. There are approximately three deaths per year in Nepal from altitude sickness, but with the right precautions there is no reason why you should become one of these statistics.
Acclimatization's the word used to describe the adjustments your body makes as it ascends. You should adjust your schedule so that you average no more than 400 meters per day of ascent above 3,000 meters. If you fail to allow time for acclimatization, you may develop symptoms of Attitude mountaineering System. The AMS may be mild enough to go away with a day's rest or if ignored may lead to death. All that is required to ensure a safe trek is basic awareness of AMS, and a willingness to rest or descend if you develop symptoms. As a result of the growing awareness of altitude problems there is only one death from AMS in Nepal out of every 30,000 trekkers and climbers. Even these deaths would be avoidable if everyone knew how to respond to AMS. There are no reliable figures for casualties among porters.