Background It is important to determine the incidence of acute mountain sickness (AMS) among workers at altitudes between 3500 m and 5000 m on Mt.Tanggula during the construction of the Qinghai-Tibet railroad.This study explored the risk factors predisposing workers to developing AMS and attempted to develop more effective ways of preventing and treating AMS.Methods A total of 11 182 workers were surveyed by completing twice daily a Lake Louise questionnaire,and a score ≥3 indicated AMS.The contributing risk factors were assessed for at least 2 months for the duration of the study in the years from 2001 to 2003.A risk model was developed by multiple Logistic regression.Standard statistical methods were used to analyze data.Results AMS occurred in 56％ of workers working at high altitudes on Mt.Tanggula.The incidence of AMS increased with increasing altitude.Rapid ascent to an altitude above 3500 m,sea-level or lowland newcomers,young people under 25 years of age,heavy physical exertion,obese person,and arterial oxygen saturation (SaO2) below 80％ were independent AMS risk factors.No significant association was found between AMS and sex or taking Rhodiola.Medical education contributed to an early diagnosis of AMS.Conclusions This study used the Lake Louise scoring system suggesting that it is a well-validated standard for field evaluation of AMS and for making an early diagnosis.These studies have described many variables regarding risk factors for the development of AMS.Risk factors which can be modified should be attended to,and the physicians should carry out check-ups and tests to identify subjects who are more at risk.Prevention consists in continuous gradual ascent,medical education,and prompt descent to avoid progression in patients with serious AMS.It is most important to effectively control the risk factors of AMS.