['Rapid ascent to altitude can result in the development of high altitude illnesses such as acute mountain sickness (AMS). This study aimed to investigate AMS symptoms in adolescents and study basic cardiopulmonary measurements at altitude.', 'Thirty-eight adolescents aged 16 to 19 years flew to 3500 m from 215 m and continued over a 23-day period to ascend to a maximum altitude of 5200 m. Each member of the expedition completed a Lake Louise Self-Assessment Questionnaire (LLSAQ) on a daily basis, and AMS was defined as a score of ≥ 3, with an associated headache. Physiology measurements included a step test, and both before and after exercise pulse oximetry, blood pressure, and pulse rate.', 'Oxygen saturation inversely correlated with altitude (P = .001). Mean pulse rate increased from 70 beats/min (± 6.5) at 215 m to 83 beats/min (± 2.2) at 3500 m (P = .01), and a rise in blood pressure with ascent was highlighted (P = .004). The majority of subjects (84%) had an LLSAQ of 3 or more on at least 1 occasion, and they tended to record higher pulse rates (P = .005) and lower oxygen saturations (P = .001). Exercise-induced drops in oxygen saturation and raised pulse rates were more prolonged in subjects with severe AMS compared with subjects not having AMS (P = .046 and P = .005, respectively).'] Is peripheral arterial desaturation further exacerbated by exercise in adolescents with acute mountain sickness?