High-altitude illness is a collective term for a cluster of acute clinical syndromes that directly consequence from rapid ascent to high altitude, viz., above 2500 m.  The acute syndromes affecting the brain include acute mountain sickness (AMS) and high-altitude cerebral edema (HACE). The current practice of high altitude medicine requires a deep knowledge of existing evidence. However, knowledge of the field is continuously evolving, and there are many gaps in the existing literature as well as areas of controversy despite existing research in the area. Each chapter begins with a real case from the author s clinical practice. After each case, a question is asked to allow the reader to reflect on clinical management before reading the answer and consolidating knowledge from experts in the field.