High mountain environments are inherently dangerous. They can be very unforgiving for those without adequate knowledge, training and equipment. Commanders and medical support personnel must understand that the interaction of environmental conditions with mission responsibilities and individual and unit characteristics can have profound negative impacts on the outcome of the mission. Adequate planning and preparedness can reduce or prevent such impacts. Preparing for and responding to environmental health hazards are critical elements to consider in the intelligence preparation of the battlefield. The purpose of this technical report is to provide updated information and guidance on the prevention and treatment of medical problems likely to be encountered by soldiers exposed to high terrestrial elevations. This information is based on research and field studies conducted by the U.S. Army Research Institute of Environmental Medicine as well as relevant material published in the medical literature.