Previous investigations suggest that ataxia is common and often one of the most reliable warning signs of high altitude cerebral edema(HACE). The aim of this study was to investigate the diagnostic role of ataxia in acute mountain sickness(AMS)and HACE among mountain rescuers on the quake areas,and in approaching the relation between AMS and HACE. After the earthquake on April 14,2010,approximately 24 080 lowland rescuers were rapidly transported from sea level or lowlands to the mountainous rescue sites at 3 750 ~ 4 568 m,and extremely hardly worked for an emergency treatment after arrival. Assessments of acute altitude illness on the quake areas were using the Lake Louise Scoring System. 73 % of the rescuers were found to be developed AMS. The incidence of high altitude pulmonary edema(HAPE)and HACE was 0.73 % and 0.26 %,respectively,on the second to third day at altitude. Ataxia sign was measured by simple tests of coordination including a modified Romberg test. The clinical features of 62 patients with HACE were analyzed. It was found that the most frequent,serious neurological symptoms and signs were altered mental status(50/62,80.6 %)and truncal ataxia(47/62,75.8 %). Mental status change was rated slightly higher than ataxia,but ataxia occurred earlier than mental status change and other symptoms. The earliest sign of ataxia was a vague unsteadiness of gait,which may be present alone in association with or without AMS. Advanced ataxia was correlated with the AMS scores,but mild ataxia did not correlate with AMS scores at altitudes of 3 750~4 568 m. Of them,14 patients were further examined by computerized tomographic scanning of the brain and cerebral magnetic resonance imagines were examined in another 15 cases. These imaging studies indicated that the presence of the cerebral edema was in 97 % of cases who were clinically diagnosed as HACE(28/29). Ataxia seems to be a reliable sign of advanced AMS or HACE,so does altered mental status. Previous investigations suggest that ataxia is common and often one often the most reliable warning signs of high altitude cerebral edema (HACE). The aim of this study was to investigate the diagnostic role of ataxia in acute mountain sickness (AMS) and HACE among mountain rescuers on the quake areas, and in approaching the relation between AMS and HACE. After the earthquake on April 14, 2010, approximately 24 080 lowland rescuers were rapidly transported from sea level or lowlands to the mountainous rescue sites at 3 750-4 568 m, and extremely hardly worked for an emergency treatment after arrival. Assessments of acute altitude illness on the quake areas were using the Lake Louise Scoring System. 73% of the rescuers were found to developed developed AMS. The incidence of high altitude pulmonary edema (HAPE) and HACE was 0.73% and 0.26%, respectively, on the second to third day at altitude. Ataxia sign was measured by simple tests of coordination including a modified Romberg test. The clinical feature The was found that the most frequent, serious neurological symptoms and signs were altered mental status (50/62, 80.6%) and truncal ataxia (47/62, 75.8%). Mental status change was rated slightly higher than ataxia, but ataxia occurred earlier than mental status change and other symptoms. The earliest sign of ataxia was a vague unsteadiness of gait, which may be present alone in association with or without AMS. Advanced ataxia was correlated with the AMS scores , but mild ataxia did not correlate with AMS scores at altitudes of 3 750-4 568 m. Of them, 14 patients were further examined by computerized tomographic scanning of the brain and cerebral magnetic resonance imagines were examined in another 15 cases. These imaging studies indicated that the presence of the cerebral edema was in 97% of cases who were clinically diagnosed as HACE (28/29). Ataxia seems to be a reliable sign of advanced AMS or HACE, so does not mental status.