Acute mountain sickness (A.M.S.) is also known as High Altitude Sickness in general may occur when people ascend too quickly normally in altitudes of over 3000 m. We ensure minimal risk by building in rest days into our trekking itineraries. Most people will feel some affect of altitude, shortness of breath and possibly light headaches, which is fairly common. Acute mountain sickness is very different and normally involves a severe headache, sickness and loss of awareness. As of this writing, there is no required immunization for travel to any of the countries where we go, however, for your protection you should consider getting vaccinated against some ailments that exist in any of these countries. To learn about prevention against malaria etc. and to find out more about the region and suggested immunizations in general, go to the following web sites: www.high-altitude-medicine.com / the Center for Disease Control and Prevention, Atlanta, GA, www.istm.org / International Society of Travel Medicine.