Résumé : Tibetans have been reported to present with a unique phenotypic adaptation to high altitude characterized by higher resting ventilation (VE) and arterial oxygen saturation (SpO2), no excessive polycythemia and lower pulmonary artery pressures (Ppa) compared to other high altitude populations. How this affects exercise capacity is not exactly known. We measured aerobic exercise capacity during an incremental cardiopulmonary exercise test (CPET), lung diffusing capacity for carbon monoxide (DLCO) and nitric oxide (DLNO) at rest, and mean Ppa (mPpa) and cardiac output by echocardiography at rest and at exercise in 13 Sherpas and in 13 acclimatized lowlander controls at the altitude of 5050 m in Nepal. In Sherpas versus lowlanders, SpO2 was 86 ± 1 vs 83 ± 2 %, mean ± SE (P NS), mPpa at rest 19 ± 1 vs 23 ± 1 mmHg (P<0.05), DLCO corrected for hemoglobin 61 ± 4 vs 37 ± 2 ml/min/mmHg (P<0.001), DLNO 226 ± 18 vs 153 ± 9 ml/min/mmHg (P<0.001), maximum oxygen uptake (VO2max) 32 ± 3 vs 28 ± 1 ml/kg/min (P NS) and ventilatory equivalent for carbon dioxide at anaerobic threshold 40 ± 2 vs 48 ± 2 (P<0.001). VO2max was correlated directly to DLCO and inversely to the slope of mPpa-cardiac index relationships in both Sherpas and acclimatized lowlanders. We conclude that Sherpas compared to acclimatized lowlanders have an unremarkable aerobic exercise capacity but with less pronounced pulmonary hypertension, lower ventilatory responses and higher lung diffusing capacity.