This study estimates bicycle helmet use among adults in the United States, examines factors associated with helmet use among adult bicyclists in 1994, and examines other safety-related practices. A telephone survey of 5238 randomly dialed households in the United States was conducted. The participants were randomly selected adult (aged > or = 18 years) respondents, and the main outcome measure was bicycle riding and helmet use in the last 30 days. We estimate that 20.2% of adults reported riding a bicycle in the 30 days preceding their interview. Of the bicyclists, 18.3% report they always wear their helmet when bicycling. Persons between the ages of 18 and 24 years had the highest proportion of bicycle riders for any adult age group (31.3%) but reported using helmets less than any other adult age group (5.1%). In univariate and multivariate analyses, age older than 24 years, female sex, higher educational level, and living in the west or northeast region of the country were associated with helmet use among adults. Helmet users were also more likely than nonusers to report a higher prevalence of other safety behaviors (ie, always wearing a safety belt, having a smoke detector in the house, and having a fire escape plan). Further efforts to increase the wearing of bicycle helmets by adults are necessary to meet the year 2000 objective of 50% helmet use. Adults should be targeted for increased helmet promotion efforts, especially those between the ages of 18 and 24 years. Increasing consistent use of helmets among adults may also help increase consistent use of helmets among children through role modeling.