The aim was to measure the incidence of high altitude headache(HAH)and to determine clinical features,as well as the relation between acute mountain sickness(AMS)and HAH through a prospective study. We conducted a questionnaire-based study among construction workers in Yushu after a serious earthquake;they were under reconstruction using a structured questionnaire incorporating International Headache Society(IHS) and AMS Lake Louise Scoring System. A total of 608 workers were enrolled after their first ascent to altitudes of 3 750~4 528 m. The results showed that 96 % reported at least 1 HAH(median 3.8,range from 1 to 10)in workers at a mean altitude of 4 250 m. The magnitude of headache was divided as mild(38 %),moderate(44 %)and severe(18 %). This study indicates that HAH is the most common symptom of acute altitude exposure and closely correlated with altitude(r=0.165,p<0.001). However,52 % of headache was one of the main symptoms of AMS, while the other 48 % was the sole symptom of HAH. On the contrary we found that 2 % of AMS without headache,thus the“painless AMS”actually existed. The clinical features of HAH are presented,and the relationship between AMS and HAH is discussed. The aim was to measure the incidence of high altitude headache (HAH) and to determine clinical features, as well as the relation between acute mountain sickness (AMS) and HAH through a prospective study. We conducted a questionnaire-based study among construction workers in Yushu after a serious earthquake; they were under reconstruction using a structured questionnaire incorporating International Headache Society (IHS) and AMS Lake Louise Scoring System. A total of 608 workers were enrolled after their first ascent to altitudes of 3 750-4 528 m. Results showed that 96% reported at least 1 HAH (median 3.8, range from 1 to 10) in workers at a mean altitude of 4 250 m. The magnitude of headache was divided as mild (38%), moderate (44%) and severe (18%). This study indicates that the most common symptom of HAH is the most common symptom of acute altitude exposure and closely correlated with altitude (r = 0.165, p <0.001). However, 52% of headache was one of the main symptoms of AMS, while the other 48% was the sole symptom of HAH. On the contrary we found that 2% of AMS without headache, thus the “painless AMS” actually existed. The clinical features of HAH are presented, and the relationship between AMS and HAH is discussed.