Trekking in Nepal is a popular recreational activity that involves approximately 45,000 persons each year. The health risk of trekking in Nepal has never been calculated. We retrospectively studied all helicopter evacuations and deaths among trekkers in Nepal between Jan 1, 1984, and June 30, 1987. A total of 148,000 persons obtained trekking permits during that time. Twenty-three persons died and 111 were rescued by helicopter. The risk of dying while trekking was 15 deaths per 100,000 trekking permits. The frequency of helicopter rescue was 75 per 100,000 trekking permits. The most frequent cause of death was trauma (11 persons), followed by illness (eight persons) and acute mountain sickness (three persons). Deaths occurred equally at all altitudes from 1000 m to over 5000 m, although the number of persons at risk at different altitudes could not be calculated. These data suggest that trekking in Nepal is a relatively safe activity, but a decision to embark on a trek in Nepal should be individualized, with an understanding of the problems related to remoteness, altitude, and illness in the absence of medical facilities.