The medical literature is replete with case reports of thromboembolic events related to high altitude exposure. Studies have shown an increased risk of thromboembolic events at high and very high altitudes. Most of these case reports and studies have been documented at altitudes between 3,000 m and 8,000 m (9,843-26,247 ft). The U.S. Air Force Academy (USAFA) rests at moderate altitude of 7,250 ft (2,210 m). This study was designed to quantify the incidence of thromboembolic events in USAFA cadets over a 5-year period and then compare the incidence of events to those in the age-matched, similarly screened midshipmen and cadet populations of the U.S. Naval and U.S. Military Academies living at sea level. Our study showed an increased incidence of thromboemoblic events in USAFA cadet outpatients compared with that in the U.S. Military Academy cadets and U.S. Naval Academy midshipmen. This implicates moderate altitude as a potential risk factor for thrombosis.