Background: Various studies have shown the deleterious effects of high-altitude hypoxia on cognitive functions, including attention and memory. Since optimal cognitive abilities may be crucial for mountain safety, this study was aimed to assess the relevance of a brief working memory test to quickly assess cognition at high altitude. Methods: A set of physiological and cognitive measurements were collected from four professional climbers at various time points during the course of an expedition to Shishapangma (8,043 m). Results: Progressive high-altitude exposure induced a classical physiological response (i.e. decreased SpO2 and increased heart rate). Except for the final ascent, no participants suffered from acute mountain sickness and perceived exertion remained low. With the exception of an increased number of night awakenings, reported sleep quality was good. No working memory decline was observed in any of the participants, even at the highest altitudes. Conclusion: Altogether, these findings show that the participants were properly acclimatized to altitude. They also highlight the technical feasibility of assessing cognitive functions all along high-altitude expeditions. The direct access of tools on a smartphone may improve mountain climbing safety.