['Although few retrospective studies of high altitude have reported that obesity might be associated with the development of acute mountain sickness (AMS), this association has not been fully studied prospectively. The aim of this study was to investigate the effect of obesity on subjects with acute high-altitude exposure.', 'Totally 262 male subjects aged 25-43 (mean 33.2 ± 9.3) years with acute high-altitude exposure were involved in this study. Among them, there are 120 obese and 142 non-obese young-middle aged male subjects. Each subject completed an AMS (acute mountain sickness) self-report questionnaire at sea level and after ascending high-altitude (3658 meters) 12 hours and 24 hours. Weight and height were measured and BMI was calculated. Vital capacity of lungs was measured. Venous blood was sampled for measuring hemoglobin at baseline. Arterial blood was taken for evaluating arterial oxygen saturation (SO2), arterial oxygen pressure (PaO2) and arterial carbon dioxide pressure (PaCO2) at baseline and 24 hours after ascending high-altitude.', 'No statistical differences were found between groups at age (p = 0.1488), hemoglobin (p = 0.5807) and vital capacity (p = 0.1806). BMI in the two groups was significantly different (p < 0.001) because it is the cut-off point of grouping. At sea level, no statistical differences were found between groups at SO2 (p = 0.1806), PaO2 (p = 0.0949), PaCO2 (p = 0.1960). But 24 hours after ascending high-altitude, SO2 (p = 0.0002), PaO2 (p < 0.001) were much lower and PaCO2 (p < 0.001) was significantly higher in obese group than in non-obese group. Comparison of AMS score: No symptom was reported at sea level in all participants (scored 0). But 12-hour and 24-hour after ascending high-altitude, the AMS scores in obese group were significantly higher than those in non-obese group (p < 0.001).'] Is obesity a risk factor for acute mountain sickness : a prospective study in Tibet railway construction workers on Tibetan plateau?