Twenty-nine cases of high-altitude pulmonary edema (HAPE) affecting visitors to Summit County, Colorado, were analyzed. The mean age of the group was 37.8 years, and all the patients were male. These results differ from previous studies and suggest that there are two varieties of HAPE. The first type (type 1, or nonresident-ascent HAPE) affects visitors to altitudes above 8,000 ft (2,439 m). At altitudes up to 11,000 ft (3,354 m), it is a disease that affects primarily adult men. The second variety (type 2, or resident-reascent HAPE) affects residents of high altitudes when they descend to an elevation below 8,000 ft (2,430 m) and then return to high altitude. This type of HAPE affects male and female residents almost equally and is a disease of childhood and adolescence.