The author reports five cases of severe acute mountain sickness on a climbing expedition to Nanga Parbat (8,125 m) in Himalaya, Pakistan. One porter developed high altitude pulmonary edema, Grade IV, at an altitude of 4,200 m, and was successfully treated with oxygen, nifedipine and descent. One of the climbers developed a moderate pulmonary edema, and two moderate cerebral edema. All of these incidents occurred above 7,000 m, and responded to descent. A case of moderate high altitude sickness is also reported. Certain pathophysiological and symptomatic features of high altitude sickness are discussed.