Despite great improvements in recent decades, the health status of American Indians continues to lag behind that of other Americans. Continued health improvement will depend largely on changes in individual behavior. However, few data exist on health risk behaviors among American Indians. We used face-to-face interviews to estimate the prevalence of some of these behaviors among American Indians 15-49 years of age in two Montana locations: on the Blackfeet Reservation and in Great Falls. The prevalence of several important health risk behaviors was higher in these populations than in adult Montana residents in general. Tobacco use was very prevalent. Fifty percent of on-reservation women, 62% of off-reservation women, 34% of on-reservation men, and 63% of off-reservation men were smokers at the time of the survey. Thirty-three percent of reservation men used smokeless tobacco. Other risk behaviors of high prevalence included acute heavy drinking (26% to 42% of men); overweight (29% to 41% of females); sedentary lifestyle (46% to 62% of all respondents); and nonuse of seat belts (64% to 79% of all respondents). Tribal leaders and the Indian Health Service are using the survey results to reduce the prevalence of behaviors harming the health of Indian people. In addition to providing valuable information about the surveyed populations, the survey served as a pilot for subsequent surveys of other American Indian groups.