Expanding athlete participation in high-altitude environments highlights the importance for a sports physician to have a good understanding of the high-altitude illness (HAI) syndromes: acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). All may occur in the setting of acute altitude exposure higher than 2500 m; incidence and severity increases as altitudes or ascent rates increase. Once HAI is recognized, proven therapies should be instituted to alleviate symptoms and avert the possibility of critical illness. Allowing for acclimatization is the best strategy for preventing HAI. Acetazolamide and dexamethasone are additional preventive measures for AMS/HACE; nifedipine, salmeterol, and phosphodiesterase inhibitors are useful in preventing HAPE. Along with the immediate hazards of HAI with altitude exposure, the sport physician also should be familiar with altitude/hypoxic training practices used by athletes to enhance fitness and performance.