The interest in mountain tracking and climbing has increased and there is a need for knowledge of altitude-related diseases. About one million non-acclimatized individuals annually frequent areas around 2,000 to 3,000 m above sea level and incur unpleasant symptoms in the form of acute altitude sickness or potentially fatal conditions such as pulmonary and/or cerebral oedema. Headache is the most prominent sign of acute altitude sickness but fainting fits, loss of appetite, hesitant gait, euphoria, or confusion also occur. Dyspnoea, cyanosis at rest, and a dry cough are signs of pulmonary oedema. Cerebral oedema may be feared when inexperienced climbers are afflicted by severe headaches, vomiting, and hesitant gait. Coma ensues relatively soon. Treatment consisting in descent to lower altitude, administration of oxygen, and possible medicinal therapy is effective if immediately introduced.