The findings suggest that the "truth" campaign may be effective in correcting youths' beliefs that most other youth are smoking and in portraying nonsmokers as independent youth who refuse to be swayed by the marketing ploys of tobacco companies. The overall aim of the campaign was to convince youth that smoking is neither normative for peer behavior nor a symbol of rebelliousness, which are both strong motivations for how youth behave. The "Think, Don't Smoke" (TDS) campaign, on the other hand, failed to impact youths' perceptions of the prevalence of smoking among their peers, perhaps because the campaign did not directly target bases for these perceptions. Given the documented link between perceived smoking prevalence among other youth and the initiation of smoking by youth, these findings show the need for a further examination of perceived smoking prevalence as a mediating factor through which media campaigns may effectively decrease youths' smoking behaviors. The study used cross-sectional time series data from the Legacy Media Tracking Surveys (LMTS), a nationally representative telephone survey of approximately 35,000 12-17 year-olds in the United States. Exposure to the "truth" campaign and the TDS campaign was measured with a series of questions on self-reported recall of the campaigns in general and of specific ads from each campaign. Perceived smoking prevalence among peers was the primary outcome variable. It was measured by using the following question: "Out of every 10 people your age, how many do you think smoke?" Multivariate models were used to assess the association between perceived smoking prevalence and exposure to the "truth" and TDS campaigns. 2 tables and 37 references