We examined the extent to which psychosocial factors, in addition to the presence of a law, are associated with the use of bicycle helmets. A mailed questionnaire was completed by 3494 children in fourth, seventh, and ninth grades in three Maryland counties: Howard County, which had a law requiring child bicyclists to wear helmets and an educational campaign; Montgomery County, which had an educational campaign but no law; and Baltimore County, which had neither. Overall, 19% of the respondents reported having worn a bicycle helmet on their most recent ride. In a multiple logistic regression, children's use of helmets in all three counties was significantly associated with their beliefs about the social consequences of wearing helmets and the extent to which their friends wear helmets. Significant interactions were also found, suggesting that in the presence of a law, an educational campaign, or both, children's use of helmets was associated more with social concerns than with parental influences or cognitive factors, such as beliefs about the need for helmets or perceptions of risk. To increase helmet use, the issues of stylishness, comfort, and social acceptability of wearing helmets need to be addressed and more widespread adoption of bicycle helmet laws should be encouraged.