Background: In recent years, the number of people visiting high altitudes has increased. After rapidly ascending to a high altitude, some of these individuals, who reside on plains or other areas of low altitude, have suffered from acute mountain sickness(AMS). Smoking interferes with the body’s oxygen metabolism, but research about the relationship between smoking and AMS has yielded controversial results.Methods: We collected demographic data, conducted a smoking history and performed physical examinations on 2,000 potential study participants, at sea level. Blood pressure(BP) and pulse oxygen saturation(SpO2) were measured for only some of the patients due to time and manpower limitations. We ultimately recruited 520 smokers and 450 nonsmokers according to the inclusion and exclusion criteria of our study. Following acute high-altitude exposure, we examined their Lake Louise Symptom(LLS) scores, BP, HR and SpO2; however, cerebral blood flow(CBF) was measured for only some of the subjects due to limited time, manpower and equipment.Results: Both the incidence of AMS and Lake Louise Symptom(LLS) scores were lower in smokers than in nonsmokers. Comparing AMS-related symptoms between nonsmokers and smokers, the incidence and severity of headaches and the incidence of sleep difficulties were lower in smokers than in nonsmokers. The incidences of both cough and mental status change were higher in smokers than in nonsmokers; blood pressure, HR and cerebral blood flow velocity were lower in smokers than in nonsmokers.Conclusions: Our findings suggest that the incidence of AMS is lower in the smoking group, possibly related to a retardation of cerebral blood flow and a relief of AMS-related symptoms, such as headache. After rapidly ascending to a high altitude, some of these individuals, who reside on plains or other areas of low altitude, have suffered from acute mountain sickness (AMS). Smoking interferes with the body’s oxygen metabolism, but research about the relationship between smoking and AMS has yielded controversial results. Methods: We collected demographic data, conducted a smoking history and conducted physical examinations on 2,000 potential study participants, at sea level. Blood pressure ( BP) and pulse oxygen saturation (SpO2) were measured for only some of the patients due to time and manpower limitations. We have recruited 520 smokers and 450 nonsmokers according to the inclusion and exclusion criteria of our study. Following acute high-altitude exposure, we examined their Lake Louise Symptom (LLS) scores, BP, HR and SpO2; however, cerebral blood flow (CBF) was measured for only some of the sub jects due to limited time, manpower and equipment. Results: Both the incidence of AMS and Lake Louise Symptom (LLS) scores were lower in smokers than in nonsmokers. Comparing AMS-related symptoms between nonsmokers and smokers, the incidence and severity of headaches and the incidence of sleep accidents were lower in smokers than in nonsmokers. The incidences of both cough and mental status change were higher in smokers than in nonsmokers; blood pressure, HR and cerebral blood flow velocity were lower in smokers than in nonsmokers.Conclusions: Our findings suggest that the incidence of AMS is lower in the smoking group, possibly related to a retardation of cerebral blood flow and a relief of AMS-related symptoms, such as headache.