At altitudes higher than the threshold altitude of 2,500 m, high-altitude diseases may occur, usually after a delay of 6 to 12 hours. Apart from the headache associated with acute mountain sickness, life-threatening cerebral edema may develop. High-altitude pulmonary edema is a non-cardiac edema that often precedes acute mountain sickness. The most important preventive measure is a slow ascent. In the case of mountain sickness a prophylactic effect can be achieved with acetazolamide or dexamethasone possible, while for high-altitude pulmonary edema, nifedipine is the first-choice drug. Immediate descent and the administration of oxygen are always indicated. Patients with a high-altitude risk are those with cardiac or pulmonary disease. Nevertheless, it is still possible for patients with coronary heart disease, hypertension or bronchial asthma to attain to high altitudes. In contrast, patients with COPD, interstitial pulmonary disease or pulmonary hypertension are at appreciably greater risk.