Acute mountain sickness (AMS) is a pathophysiological symptom complex that occurs in high altitude areas. The AMS prevalence is reportedly 28% on Jade Mountain, the highest mountain (3952 m) in Taiwan. We conducted this study owing to the lack of annual epidemiological data on AMS in Taiwan. Between April 2007 and March 2008, 1066 questionnaires were completed by trekkers visiting Paiyun Lodge on Jade Mountain. Information in the questionnaire included demographic data, mountaineering experience, AMS history, and trekking schedule. Weather data were obtained from the Central Weather Bureau of Taiwan. The Lake Louise AMS score was used to record symptoms and diagnose AMS. The chi-square test or the Student t test was used to evaluate associations between variables and AMS. In our study, the AMS prevalence was 36%. It increased significantly at different rates at different locations on the Jade Mountain trail and varied significantly in different months. Rainy weather tended to slightly increase the incidence of AMS. A lower incidence of AMS was correlated with hig-altitude trekking experience or preexposure (p < 0.05), whereas a higher incidence of AMS was correlated with a prior history of AMS (p < 0.05). The trekkers with AMS were significantly younger, ascended faster from their residence to the entrance or to Paiyun Lodge, and ascended slower from the entrance to the Paiyun Lodge (p < 0.05), but the differences lacked clinical significance. No differences in the incidence of AMS based on blood type, gender, or obesity were observed. The most common symptom among all trekkers was headache, followed by difficulty sleeping, fatigue or weakness, gastrointestinal (GI) symptoms, and dizziness or lightheadedness. In conclusion, the AMS prevalence on Jade Mountain was 36%, varied by month, and correlated with trekking experience, preexposure, and a prior history of AMS. The overall presentation of AMS was similar to that on other major world mountains.