OBJECTIVE: To determine why people do or do not wear helmets while bicycling. METHODS: A survey was conducted from August through October 1999. Two survey areas were chosen for this study: local public schools and paved bicycle trails. For the school arm of the study, 3 public elementary, middle, and high schools were selected from 3 different regions of Rochester, Minnesota, for participation in the study. For the bicycle arm of the study, 3 paved trails located in southeastern Minnesota were selected. A total of 2970 surveys were distributed to the public school system, and 463 surveys were collected from bicyclists on the paved bicycle trails. The survey population was split into 3 age categories for analysis: child (7-10), adolescent (11-19), and adult (older than 19). RESULTS: Of the 2970 surveys distributed to Rochester public schools, 2039 (69%) were returned for analysis. Seventy-eight of the surveys that were completed in the public school system were discarded for the following reasons: age <10 years (35), insufficient completion (24), and selection of every reason for not wearing a bicycle helmet (19). A total of 463 surveys were completed on the 3 paved bicycle trails. One survey from the paved bicycle trail arm of the study was discarded because of insufficient completion. The total number of surveys used for statistical analysis was 2424. The distribution of male (52.7%) and female (47.3%) participants was similar. No significant difference in bicycle helmet use was found between genders. The age groups with the highest rate of bicycle helmet use were 50 to 59 years (62%) and older than 59 years (70%). The age groups with the lowest rate of bicycle helmet use were 11 to 19 years (31%) and 30 to 39 years (30%). The most common reasons given for not wearing a bicycle helmet were "uncomfortable," "annoying," "it's hot," "don't need it," and "don't own one." Bicycle helmet use was significantly influenced by peer helmet use in all 3 age groups. Children also were more likely to wear a bicycle helmet when their parents wore bicycle helmets. A majority of respondents in all 3 age groups indicated that bicycle helmets provided either "moderate" or "great" protection from head injury, although significantly more adults (65.9%) than adolescents (43.9%) believed that the protection afforded by bicycle helmets was "great." Despite this belief, a majority of adolescents and adults indicated that there was only a "slight risk" of head injury when bicycling without a helmet. Participants in all 3 categories were more likely to wear a bicycle helmet when they indicated either that there was a "great risk" of head injury when bicycling without a helmet or that helmets provided "great protection" from head injury. Adolescents and adults who believed that bicycling without a helmet put one at "great risk" for head injury also were more likely to indicate that helmets provided "great protection" from head injury. CONCLUSIONS: The prevalence of bicycle helmet use remains low despite research indicating the high level of head injury risk when bicycling without a helmet and the significant protection afforded by bicycle helmets. With the information provided by this survey, a well-designed intervention to increase the use of bicycle helmets can be implemented. Suggestions for a campaign to promote an increase in bicycle helmet use include focusing efforts on males and females between 11 and 19 years and 30 and 39 years of age; educating the public on new bicycle helmet designs that address comfort, ventilation, and fashion; educating adolescents on the significant protection from head injury afforded by bicycle helmets; and educating the public on the risk and severity of head injury associated with bicycling without a helmet. The influence of parents and peers on bicycle helmet use may be targeted through education and statements such as, "If you wear a bicycle helmet, you are not only protecting yourself, you are also helping to protect your friends and/or children." bicycle, helmet, injury, accident, prevention.