High-altitude illness is a growing concern in sports medicine that affects persons shortly after they have climbed to a new high-altitude level to which their body is not acclimatized. With the increasing popularity of extreme sports, such as high-altitude mountaineering, skiing, and snowboarding, the incidence of complications arising from sports activities at high altitudes is increasing. High-altitude pulmonary edema and high-altitude cerebral edema are potentially fatal conditions. The study of high-altitude muscle physiology has broad ramifications in creating training programs for elite endurance athletes. A thorough understanding of the pathophysiology, presentation, treatment, and prevention of high-altitude illness is necessary for the treatment of these patients.