This study examines how the American Legacy Foundation's "truth[R]" campaign and Philip Morris's "Think. Don't Smoke" (TDS) campaign have influenced youth's tobacco-related attitudes, beliefs and intentions during the first 3 years of the truth campaign. We use data from eight nationally representative cross-sectional telephone surveys of 35,074 12- to 17-year olds to estimate cross-sectional time series logistic regressions that assess the association between recall of truth and TDS and attitudes, beliefs, and intentions toward smoking. An alternative measure of exposure to TDS was also used. Findings indicate that exposure to truth advertisements (ads) was associated with steady positive changes in attitudes, beliefs and intentions to smoke, whereas exposure to Philip Morris ads was associated with more favorable beliefs and attitudes toward the tobacco industry. Our findings suggest that well-executed antismoking campaigns can positively and consistently change youth's beliefs and attitudes, whereas a tobacco industry-sponsored campaign can have a counterproductive influence. (Contains 1 table and 1 figure.)