High-altitude cerebral oedema is one of the three forms of altitude sickness and is considered one of its most serious complications. Its incidence is relatively low, but its rapid progression and worsening symptoms make it a life-threatening condition that requires immediate medical attention. The growing popularity of high-altitude tourism means that knowledge about altitude sickness and high-altitude cerebral oedema should be promoted not only among medical professionals but also among ordinary tourists planning high-mountain expeditions. The following paper, which is a narrative review describing high-altitude cerebral oedema, discusses the key pathogenetic elements of this condition, including molecular mechanisms resulting from exposure to hypobaric hypoxia, blood-brain barrier dysfunction, increased vascular permeability, and the development of both vasogenic and cytotoxic oedema. Epidemiological data and risk factors are presented, followed by the spectrum of clinical manifestations, ranging from non-specific, mild symptoms that may coexist with an episode of acute mountain sickness to ataxia, impaired consciousness, and other severe neurological signs. The paper addresses diagnostic issues, with particular emphasis on the usefulness of imaging tests, specifically magnetic resonance imaging, in the process of confirming the diagnosis. Finally, the role of rapid implementation of appropriate therapy, consistent with current medical knowledge and consisting of altitude reduction, oxygen therapy, administration of steroids, and, in difficult conditions, the use of a portable hyperbaric chamber, is emphasised. High-altitude cerebral oedema remains a challenge that should always be managed by an interdisciplinary team; however, further research is needed to deepen our understanding of the pathophysiology, diagnosis, and treatment of this condition.